Its a common mis-understanding that many Buy to Let investors think that they can rollover the gains under business asset rollover reliefs.
Residential Property Investment is not a trading activity, whenever you sell a property that isn’t your main residence you will be liable to capital gains tax.
If you want to release cash from your property portfolio its better to consider other options such as re-financing to take advantage of capital growth.
Also joint ownership (particularly between spouses) will increase the available Capital Gains Allowance you have, individuals currently have £11,000 per year. This allowance might cover your gain?