Solicitors are currently faced with a bit of a quandary when it comes to exchange and completion timings.
In normal times, banks like 7 working days at most advance warning of completion. You send in a certificate signed by a partner at the firm, telling the bank the property is good and we want funds on "day before completion" please.
You would therefore ideally look to exchange 2 weeks prior to completion. This allows the money to be sorted, battery, removals etc etc.
At the moment however there are mortgage offers being pulled thanks to changes in lending criteria and borrowers' circumstances.
It would be DEVASTATING to exchange one day and have your offer rescinded the next. Devastating.
THIS is why sols are now going for the least worse option of shortening the time between exchange and completion / to reduce that risk.
There's also the risk of someone getting poorly or having to isolate as per test and trace guidelines, but if all parties in the chain agree - and I've not seen it yet, and property is my thing - then a Covid clause might be the way forward for that. But it doesn't include circumstances where offers are pulled.
OP there's a greater chance now that your buyers' offer and yours (if you have one) would be pulled as banks are in effect "catching up". They are now starting to really pull products. There is NOTHING to stop any lender pulling a loan offer at any time, even post exchange.
Covid Clauses are untested and some I've seen are flimsy at best, even my own isn't water right. But as I said, in any of the chains I've been dealing with not all sols have agreed to use it and therefore NONE of us can use it.
Imagine if you all had exchanged. As it turns out it looks like you would have served your notice and all likely agreed to the bottom of the chain's lender's timetable of 9 days. And you can all do that - alter the terms as long as you all agree. But you would still be in the same position, except this time you'd be worried about your deposit being forfeit and then having to chase the buyers for costs through the courts.
It's so so unfortunate how it all turned out, but what has happened here is exactly why your sol was going for the short exchange / completion turnaround...