Lease Premiums

Hello,

I have a question about lease premiums.

On 1 October 2022, Sou grante a 25-year lease of a freehold property in return for a premium of £20,000.
What is Sou’s assessable property income for the tax year 2022/23 in respect of this lease premium?

Answer:

(51-25)/50 x 20,000 = £10,400

My doubt:

In which situations should we divide the above computation for the number of years of lease?

Thanks,
Filipa