Contract of sale

Canon92

I'm currently going through a nightmare house move and looking for some advice as I now can't contact my solicitor until Tuesday.
After a few weeks we were able to agree upon a completion date of June 2nd (next Wednesday). We are in a 4-person chain with a FTB below us. 
Contracts were to be exchanged today but this didn't happen because nobody was able to contact the solicitor at the top of the chain.
Anyway, our vendors are insisting we try again Tuesday to enable us to still complete on Wednesday. Our solicitor has agreed to attempt the exchange again on Tuesday.
My concern is I have been copied into an email earlier this week where our lender has stated our solicitor must 'send them a copy of the signed Contract of Sale' by no later than 12:00 on the 1st for funds to be ready for the 2nd.
I should have asked her before she finished today if this has been done or if it comes from the exchange of contracts, but by the time I realised it was too late and she has finished work for the weekend. So my question is does the 'signed contract of sale' come from exchange and therefore it's very unlikely we are going to meet that deadline?
The reason I want to know sooner rather than later is because I can get my deposit back on my removals company if I call them today/tomorrow, but not if I leave it until Tuesday.