diff --git a/lib/spree/paypal_express.rb b/lib/spree/paypal_express.rb
index 2ca99ce..52de761 100644
--- a/lib/spree/paypal_express.rb
+++ b/lib/spree/paypal_express.rb
@@ -1,11 +1,12 @@
-# WARNING: the details of UK tax and my site's shipping are a bit hard-coded here for now
 # aim to unpick this later
 module Spree::PaypalExpress
   include ERB::Util
   include Spree::PaymentGateway
+  include ActiveMerchant::RequiresParameters 
+
 
   def fixed_opts
-    { :description             => "Goods from a Spree-based site", # site details...
+    { :description             => "Goods from #{Spree::Config[:site_name]}", # site details...
 
       #:page_style             => "foobar", # merchant account can set named config
       :header_image            => "https://" + Spree::Config[:site_url] + "/images/logo.png", 
@@ -15,9 +16,16 @@ module Spree::PaypalExpress
 
       :allow_note              => true,
       :locale                  => Spree::Config[:default_locale],
-      :notify_url              => 'to be done',                 # this is a callback
+      :notify_url              => 'to be done',                 # this is a callback, not tried it yet
 
       :req_confirm_shipping    => false,   # for security, might make an option later
+
+      # :no_shipping     => false,
+      # :address_override => false,
+
+      # WARNING -- don't use :ship_discount, :insurance_offered, :insurance since 
+      # they've not been tested and may trigger some paypal bugs, eg not showing order
+      # see http://www.pdncommunity.com/t5/PayPal-Developer-Blog/Displaying-Order-Details-in-Express-Checkout/bc-p/92902#C851
     }
   end           
 
@@ -25,12 +33,13 @@ module Spree::PaypalExpress
   # might be able to get paypal to do some of the shipping choice and costing
   def order_opts(order)
     items = order.line_items.map do |item|
+              tax = paypal_variant_tax(item.price, item.variant)
               { :name        => item.variant.product.name,
                 :description => item.variant.product.description[0..120],
                 :sku         => item.variant.sku,
                 :qty         => item.quantity, 
-                :amount      => item.price - 0.15 * item.price,   # avoid some rounding err, more needed
-                :tax         => 0.15 * item.price, 
+                :amount      => item.price - tax,   # TODO: test if ok on multi-qty orders
+                :tax         => tax,
                 :weight      => item.variant.weight,
                 :height      => item.variant.height,
                 :width       => item.variant.width,
@@ -42,47 +51,65 @@ module Spree::PaypalExpress
              :order_id          => order.number,
              :custom            => order.number,
 
-             # :no_shipping     => false,
-             # :address_override => false,
-
              :items    => items,
              :subtotal => items.map {|i| i[:amount] * i[:qty] }.sum,
-             :handling => 0,
              :tax      => items.map {|i| i[:tax] * i[:qty]}.sum
 
-             # WARNING -- don't use :ship_discount, => :insurance_offered, :insurance since 
-             # they've not been tested and may trigger some paypal bugs, eg not showing order
-             # see http://www.pdncommunity.com/t5/PayPal-Developer-Blog/Displaying-Order-Details-in-Express-Checkout/bc-p/92902#C851
            }
-
-    opts[:email] = current_user.email if current_user
-
     opts
   end
 
-  def all_opts(order)
-    shipping_cost = NetstoresShipping::Calculator.calculate_order_shipping(order)
-    opts = fixed_opts.merge(:shipping => shipping_cost).merge(order_opts order)
+  # hook for supplying tax amount for a single unit of a variant
+  # expects the sale price from the line_item and the variant itself, since
+  #   line_item price and variant price can diverge in time
+  def paypal_variant_tax(sale_price, variant) 
+    {}
+  end 
 
-    # WARNING: paypal expects this sum to work (TODO: shift to AM code? and throw wobbly?)
-    # however: might be rounding issues when it comes to tax, though you can capture slightly extra
-    opts[:money] = opts.slice(:subtotal, :shipping, :handling, :tax).values.sum
-    if opts[:money] != order.total
-      raise "Ouch - precision problems: #{opts[:money]} vs #{order.total}"
+  # hook for easy site configuration, needs to return a hash
+  # you probably wanto over-ride the description option here, maybe the colours and logo
+  def paypal_site_options(order) 
+    {}
+  end
+
+  # hook to allow applications to load in their own shipping and handling costs
+  # eg might want to estimate from cheapest shipping option and rely on ability to
+  #   claim an extra 15% in the final auth
+  def paypal_shipping_and_handling_costs(order)
+    {}
+  end
+
+  def all_opts(order)
+
+    opts = fixed_opts.merge(order_opts                         order).
+                      merge({ :shipping => 0, :handling => 0 }      ).
+                      merge(paypal_shipping_and_handling_costs order).
+                      merge(paypal_site_options                order)
+
+    # add the shipping and handling estimates to spree's order total
+    # (spree won't add them yet, since we've not officially chosen the shipping method)
+    spree_total = order.total + opts[:shipping] + opts[:handling]
+
+    # paypal expects this sum to work out (TODO: shift to AM code? and throw wobbly?)
+    # there might be rounding issues when it comes to tax, though you can capture slightly extra
+    opts[:money] = opts.slice(:subtotal, :tax, :shipping, :handling).values.sum
+    if opts[:money] != spree_total
+      raise "Ouch - precision problems: #{opts[:money]} vs #{spree_total}"
     end
 
+    # prepare the numbers for the gateway
     [:money, :subtotal, :shipping, :handling, :tax].each {|amt| opts[amt] *= 100}
     opts[:items].each {|item| [:amount,:tax].each {|amt| item[amt] *= 100} }
 
+    # suggest current user's email or any email stored in the order
+    opts[:email] = current_user ? current_user.email : order.checkout.email
+
     opts
   end
 
   def paypal_checkout
-    # need build etc? at least to finalise the total?
-    gateway = paypal_gateway
-    @order.update_totals
-  
     opts = all_opts(@order)
+    gateway = paypal_gateway
     response = gateway.setup_authorization(opts[:money], opts)
 
     gateway_error(response) unless response.success?
@@ -91,9 +118,8 @@ module Spree::PaypalExpress
   end
 
   def paypal_finish
+    opts = { :token => params[:token], :payer_id => params[:PayerID] }.merge all_opts(@order)
     gateway = paypal_gateway
-    opts = { :token => params[:token],
-             :payer_id => params[:PayerID] }.merge all_opts(@order)
     info = gateway.details_for params[:token]
     response = gateway.authorize(opts[:money], opts)
 
@@ -141,14 +167,15 @@ module Spree::PaypalExpress
     payment.creditcard_txns << transaction
 
     order.user = current_user
-
     order.save!
-
     order.complete  # get return of status? throw of problems??? else weak go-ahead
-    session[:order_id] = nil if order.checkout_complete
-    redirect_to order_url(order, :checkout_complete => true, :order_token => session[:order_token])
-  end 
 
+    flash[:notice] = t('order_processed_successfully')
+    order_params = {:checkout_complete => true}
+    order_params[:order_token] = @order.token unless @order.user
+    session[:order_id] = nil if @order.checkout.completed_at
+    redirect_to order_url(@order, order_params) 
+  end 
 
   def do_capture(authorization)
     response = paypal_gateway.capture((100 * authorization.amount).to_i, authorization.response_code)
@@ -167,17 +194,20 @@ module Spree::PaypalExpress
 
   private
 
-  # copied from main spree code, and slightly tweaked
+  # create the gateway from the supplied options
   def paypal_gateway
-    #? return Spree::BogusGateway.new if ENV['RAILS_ENV'] == "development" and Spree::Gateway::Config[:use_bogus]
-    paypal_gw = ::Gateway.find_by_name("Paypal Express UK")
-    gateway_config = GatewayConfiguration.find_by_gateway_id(paypal_gw.id)
-    config_options = {}
-    gateway_config.gateway_option_values.each do |option_value|
-      key = option_value.gateway_option.name.to_sym
-      config_options[key] = option_value.value
-    end
-    gateway = gateway_config.gateway.clazz.constantize.new(config_options)
-  end
+    gw_defaults = { :ppx_class => "ActiveMerchant::Billing::PaypalExpressUkGateway" }
+    gw_opts     = gw_defaults.merge(paypal_site_options @order)
+ 
+    begin 
+      requires!(gw_opts, :ppx_class, :login, :password, :signature)
+    rescue ArgumentError => err
+      raise ArgumentError.new(<<"EOM" + err.message)
+Problem with configuring Paypal Express Gateway:
+  You need to ensure that hook "paypal_site_options" sets values for login, password, and signature.
+EOM
+    end 
 
+    gateway = gw_opts[:ppx_class].constantize.new(gw_opts)
+  end
 end