Dear *****, thank you for your response.
No, I have no idea why they offered this - that's why I'm so confused (I did not expect this).
This is what the letter says:
"I am pleased to advise that our clients are willing to offer you an extension on the following terms:
1. No lease extension premium payable
2. New lease of 99 years from now
3. Your annual ground rent to be £300, reviewed every ten years with reference price index (NB - at the moment I pay £75/year)
4. No landlord's valuation costs
You would still be required to pay the landlord's legal costs for drafting of the new documents. You will also be responsible for LMP administration costs of £292 (incl VAT)."
This is it - "LMP" is the freeholder's agent (I pay ground rent to them).
Thank you very much.