Hello Michael, I am Keith and pleased to be able to help you with your problem.
As the property is held jointly you would be Joint Tenants and assumed to own the property 50/50. If however, there is evidence to the contrary and each hold different shares in the property then you would be Tenants in Common. In either event the 27K quid received would be split between you, typically half each. This is treated as follows [source Robinson Reed Layton, Chartered Accountants and Chartered Tax Advisers]:
'For leases of between two and 50 years, the treatment is more complicated, and works by splitting the premium into two payments – one of rent, and the other of a capital sum. The calculation is quite simple. Take the number of complete years in the term of the lease, deduct one year, and multiply the result by 2%. This gives you the capital gains element of the premium, and the balance of the payment is rent.
For example, if Mr Jones pays a premium of £10,000 for a twenty-one year lease of a shop, the capital element is £4,000. Twenty times 2% is 40%, and 40% of £10,000 is £4,000. The other £6,000 is treated as rent.'
Thus of the 27K, 4.86K will from part of the Capital Gains Tax (CGT) computation and 22.14K will be additional rental. This would be half each so an extra 11.07K would have to be declared as rental along with normal rents on your annual self assessment tax return. As you will have received income and a capital gain upon which tax has not been charged you will have to self assess and declare for then tax year (14/15) in which you received the premium. You do have an Annual Exempt Amount of 11K (14/15 rates) which may well remove any likelihood of a CGT assessment.
You should contact your tax office, you will find their address on your notices of tax coding, for them to send out a form for you to complete or you can do it in line if you prefer.
I do hope I have been of assistance. Don't hesitate to follow up if you are in any doubt.