I am thankfully not a tax specialist but there has been a deviation from reality in the responses the OP has received here. Although the OP may have been and gone to the UK by now, I am answering these well-meaning comments for anyone who comes across this thread when doing VAT research in the future.
there's a service charge that you must pay which makes the refund somewhat less.
Not quite right. Retailers have the right to levy an admin fee, and even in expensive stores such as Harrods (where Apple products can be purchased)
they do not charge a fee. Even if there was a charge we are talking 14% off instead of 15% ie saving value will not plummet.
U need your passport and proof of address to do this but any business has the right to refuse.
If the retailer is part of the VAT Retail Export Scheme it will give you the refund. This comment gives the impression that an assistant may arbitrarily refuse to fill out a VAT form with you depending on how he is feeling that day. Sorry, that is false. If the physical Apple Stores offer the facility they will not withdraw it because you, for example, voted Bush.
You can get the forms from the tax office to claim back the vat if you really want to.
If you want to re-claim the VAT, the necessary forms must be filled out in the presence of the retailer.
I thought businesses can refuse to do it for you on the spot but you still have the option to go to the customs area at Heathrow and fill out the forms there. And then there is no service charge, either.
Again, if the business is not part of the VAT Retail Export Scheme, or the goods are bought online, no refund.
You will find it very hard to get the VAT back. It is generally only shops specializing in selling to tourists that are equipped to fill out the paperwork you need. The Apple Stores are not tourist shops.
I don't know where you got this impression but it is pretty much completely untrue. Most tourist shops in London will be part of the VAT refund scheme but this does not equate to mainly tourist shops being VAT scheme members. Large department stores - John Lewis, Selfridges are part of the scheme.
See this link for the lowdown:
http://customs.hmrc.gov.uk/channelsPortalWebApp/channelsPortalWebApp.portal?_nfpb=true&_pageLabel=pageTravel_ShowContent&id=HMCE_CL_000141&propertyType=document#P11_904