(currently I have a previous working system where the ecart shipping rules allow for dectection for a product to be either a regular product (£7 default shipping) and a gift voucher (99pence shipping) and i got a checkbox that allows a sessions to be stored to calculate free shipping if customer choses to collect from shop. (but this approach needs to be modifed due to client wanting the customer to have a third choice (the newly included £4 shipping option as stated at the beginning). 
ok, so how is the current rule configured, if you provide details on how it is currently set up, i can give you details to modify it.
