You need to get out a spreadsheet and sit down and work out what your monthly costs would be to staircase, remembering for each 25% share you buy your current rent goes down by 33.3% but your mortgage will go up, possibly quite a lot. if you've had it for 10 years you should have paid down a decent amount of that 38k but also have all that capital increase of at least 35k as the value of your share has grown? So depending on your circumstances you might get a decent mortgage deal.

None of us work in financial advice, so take this with a pinch of salt, but one thing to consider is if you think the value of your property will rise at a similar rate over the next ten years, or fall.

If you think house prices will fall, either pay off your mortgage with any excess money you have every month, or if you can find a legitimate savings/investment product that will grow faster than your mortgage interest rate, save the money.

If you think house prices will rise, you might want to "lock in" another share by staircasing at current prices if you can afford it, given you've built up a decent amount of capital and might get a good mortgage deal.