This seems a pretty steep increase - it’s not illegal for them to do this as their previous figure was only an estimate and if the process took much longer than expected then I guess they have incurred higher costs. You should ask them for detailed reasons why they are asking for more and then you can challenge them if you think they are unreasonable.

What does your client care letter say about fee reviews? The answer will be there. Either way I think they probably should have told you prior to exchange of contracts!

Ask for a breakdown.

Have a discussion with them about it and ask for a breakdown. It’s likely they’ve incurred more time than anticipated but they should have kept you updated on where they were with fees etc.

It’s probably a bit of give and take if you’ve got an ongoing relationship and want to work with them in the future.

Your solicitor would well just be assuming that as you've worked with them several times before, you're happy with their billing and trust them to bill your fairly based on the work undertaken.

This is how retained billing often works, especially at scale. Admittedly you would expect them to be advising you of costs when it's more than doubled, at any rate.

In my experience, legal bods tend to just assume you know that anything they do over and above is chargeable, so don't explicitly advise you as such unless you ask. With your case, they've probably assumed you'd know, and would ask if interested, due to the other party creating more work for them.

It will almost certainly be in their terms that they do this, anyway...so all you can really do is express your dissatisfaction that they have not been advising you of the increased costs and maybe see if they'll reduce it somewhat. Possibly suggesting that you might be looking elsewhere in teh future...though they're almost certainly well within their rights, so you don't actually want to burn a relationship, more just suggest that it's in their best interests for future business to keep you happy right now.

You need to be clear of what is an 'estimate' and what is a 'quote'. You state you were quoted "around" £2000 but if it's not a WRITTEN quote then it's not a quote but an estimate. You've probably got a very good and conscientious solicitor who didn't anticipate the other side were going to create more work. Best not to fall out over such issues. Your solicitor will most likely be happy to show you all the work that was involved that created the cost.