Section 20 on leasehold flat

I'm trying to buy a flat. Neither me or the seller are in a chain and were both hoping for a quick sale.

Near the end of the process my solicitor discovered a Section 20 had been issued to the block of flats but it hasn't got past stage 1. It was issued nearly a year ago and the only information we can get from the freeholder is that the works are on hold and there's no cost estimates.

They've provided just very basic information about the work intended (repairing concrete balustrades on walkways). This could end up costing loads!

I love the flat and both me and the seller are keen to progress but obviously it would be a big risk and it's had to be referred to my mortgage lender who I assume is going withdraw the offer until a solution can be found.

The freeholder has basically made the entire block incredibly difficult to sell. How long are they allowed to keep people in limbo and is there any way of pushing for more info? If we had a cost estimate then me and the seller could work out a solution but costs for work like this could vary dramatically so it's hard to know what to do.