Land Registry - Old address on Title register, new address on Title plan

Glover1862

Please can someone help, we are near the end of purchasing a flat, typically the solicitors have been really slow, now our solicitor is saying the the Title Register has a different address on it (old address), however in 2015 it looks like the address and postcode were changed,  no one recognises the old postcode as it looks to be obsolete. The solicitors say the mortgage must match the title register, our mortgage brokers says the whole application will need to be redone and the fixed rate we were on has moved up 0.5%, it was a real struggle to get a mortgage and we can't risk trying to get a new one, plus the broker is saying how can he process a mortgage application on an address that no longer exists. 

Ideally, we want the sale to proceed and sort out the LR title register later and pay any fees to do it, it's very odd as the title plan shows the new building number and title register shows the old!!

The solicitors is saying it could take ages to correct and costs will be passed to us, we want to ditch this solicitors and use someone else for further work, can anyone offer help on how we can proceed using our current mortgage offer and just get the sale over line and deal with Land registry later, solicitor saying we can't do that, but not offering any real hlep how to progress.