NatWest can do something similar. They will usually just charge £100 for now but, if you're on a fixed term deal, they will want you to switch at the end of the term.

http://www.natwest.com/personal/mortgages/g4/common-questions.ashx#what_if_i_want_to_rent_out_my_place

If you don't want to phone up to ask the question "what if", you should certainly check the lender's web site to see if there is information there.