Thanks everyone for being so lovely!
Apparently the only way to save the chain is if we go into a holiday letting for two weeks.... with us being the only ones with young kids to get to school etc! The retired couple we are buying from and our buyer who has one grown up child couldn't possibly stay with family or rent for a few weeks 
However, we are not prepared to lose the perfect house and to have gone through the last 7-8 months of shit for nothing just for the sake of 2 weeks...
So we have very reluctantly agreed to complete on our sale on 29th so our buyer doesn't lose her buyer at the start of the chain and to then stay in a holiday let until we can complete on the new house on 12 September. HOWEVER, we have only agreed to do this IF we all exchange contracts next Tuesay. Otherwise we have no time to sort out holiday let and storage. Plus we will need to put our dog in kennels for two weeks.
Going to costs us about £2500 in total with shortage, kennels, holiday rent etc but I suppose we would have to pay this in mortgage fees and solicitor fees if we have to find another property anyway....
This means our seller seller can still have Monday to read all the paperwork and still have three weeks to get funds drawn down.
Our solicitor is chasing up and down the chain to make sure everything is ready to exchange on Tuesday. Apparently there is one thing outstanding at the very top of our chain but she has stressed the urgency and they are trying to sort it today.
Clinging on by fingernails!!!! Will only come together if our sellers seller agrees to exchange as soon as he gets back from holiday!
Keep everything crossed for me 