A lot depends on the period of the lease. But if it’s £4 it’s probably a very long lease.
Sounds like our first house, in Eltham, London.
There was initially a 999 year lease on the property, I think we had something like 950 years left on it. Ground rent of £4 per year. We were offered to buy the lease for about £700. (These are approx figures, it was about 35 years ago).
I couldn’t see any benefit in paying 175 years of ground rent for the freehold.
We had absolutely no problem selling the house on. Buyers weren’t worried about an over 800 year lease.
In your case, I don’t see any benefit to you, you’d still be paying the £4 each year, but just direct.
For tidiness, it might be nice to have the lease, maybe £200, but watch out for legal fees/ arrangement fees.
Personally, I wouldn’t bother.