This is the wrong idea. You should pay the profits each year as income and use the net receipts to pay down your mortgage.
As the OP has the benefit of a PAYE job and a Ltd company, there are options to build up reserves in the company and look at options such as Entrepreneurial relief, Retirement relief , termination payments pension funding, and liquidation at CGT rates etc to get funds out of the company in a much more tax efficient manner. Build up the reserves in the company and invest in the company name if you so wish ( i.e. treat it as a pension to generate some returns ) and at some point down the road you may well be able to generate a large lump sum to materially pay down mortgage debt rather than in increments when you have already paid an effective tax rate of 50%.
As the reserves in the company are liquid you have the flexibility to change your strategy if required and pay yourself a salary in any year you so wish.
The tax efficiency will reduce the time it takes to become mortgage free instead of paying down debt out of after tax funds.
Just a different approach to meet the OP's objectives