Clearly will be seeking professional advice but wanted to shoot this out before going too far down the road.

In 2012 we bought a flat for a relative jointly with family for £130k. It's a freehold flat so getting a mortgage was fun so the other party took the mortgage on their property (interest only) and it's sat there ever since.

We are now in the position to buy them out and take sole ownership but it's got me thinking about tax liability, specifically stamp duty. The deal would be:

- We repay the £130k mortgage that currently is on their property, to recap the property in question (the flat) is not mortgaged
- We pay them £55k for their share for the increase in value (current flat value is approx £240k)

..so the only 'cash' changing hands is £55k, so is that the amount considered for stamp duty? Or does the mortgage amount come into it too? If the former we're well under the £125k ceiling of course.

Thanks!
Adam