Often when a client takes a mortgage to buy a home in the UK the opportunity to work and live abroad is not even a consideration. This means that no forward planning was in place to ensure that the UK lender selected allows you to move out of your property. Whilst the lender cannot physically stop you from moving abroad, they can, under the terms of the mortgage agreement, request their money back.
A further issue can arise if you wish to rent out your property in your absence. A traditional UK mortgage does not provide you with permission to rent your property out. Doing so contravenes the terms of your mortgage agreement, and again the lender can request their money back.
The simple answer to these issues is to remortgage to a lender and scheme designed specifically for expats, the lender will be aware and happy with your residential status and will provide you with permission to let your property, usually for a 3 to 5 year initial period.