When you Purchase a property with the Right to Buy housing Scheme, for the term of the mortgage they will put a condition that you cannot sell the house without incurring a charge so that wealthy people aren’t tempted to use the scheme to line their pockets. You are though able to change the creditor without any effect on paying back the council, most lenders do not have an issue with Right to Buy Lending.
When remortgaging you will get a charge from the council though (this is encase you default on the remortgage), It wont stop the remortgage taking place but it will complicate it this is all to prevent early selling or any scamming on the system. The council will not stop you remortgaging but will and do have the right to stop any early selling of the property.