I would suggest you get legal advice, before you approach the freeholder. No point getting the leaseholders permission as that is you.
It will be expensive, the lower the lease is.

I would suggest buying the freehold if that is possible.

I live in a block of flats we are leaseholders but also own the freehold. We extended our lease from about 90 years to 999 years.

I can't remember but there is some sort of right to buy for leaseholders. If you are planning on staying where you are this would be better in the long run. Aa the owner of the freehold you can then write your own lease you would also control ground rent this is just a device for the freeholder to extract more money.

If you have neighbours I would suggest you approach the freeholder as a group. The way it works is you set up a company that owns the freehold each dwelling has 1 share in that company you can then write your own lease and make whatever rules through the company.

If you are just planning to extend the lease I might be wrong but I think you will need the permission of the freeholder to convert a 1 bed into a 2 bed? They may refuse or ask for an additional payment.

One more point

Thanks for your helpful comments,its a big block of flats in Croydon so not much chance of buying the freehold .Probably makes sense to get lease extented first before adding value with second bedroom but qill get some legal advice thanks all .

I am an estate agent. Regardless of whether it's a one or two bed, if you're looking to sell it and the lease is under 70 years, you Defo need to extend as mortgage companies for the buyer won't lend on it. It needs to be really 99years or above.

SUPPORTING PALACE SINCE 1986

Defo going to extend the lease as quite low ,and know its going to cost around the £40g mark to increase , but my issue is turning it into a two bed before or after , but looks likely to be best after extending cheers