Realistically, how quickly can we complete?

[cheapandcheerful]

We found a house at the weekend (finally, after our previous place falling through)...
Our buyer wants to complete around Jan 5th (obviously not going to happen!) but what is the quickest we can realistically expect to complete our purchase, assuming nothing is wrong with the survey and bearing in mind the xmas period?

I'm reeeeeeally ready to go now!

Ah - that's bad news. What did they lie about?

We went from offer to exchanging contracts in 3 weeks on our current house but were pushing solicitor every day or two and it took some doing

a small matter of them being ready to complete on 21st Nov and asking us to reduce our price because we weren't, when it turns out now they haven't got their mortgage in place and so won't be able to complete until the new year now We have turned everything around in 3 weeks. they've had since 1st Aug when we accepted their offer!

Well they need to get their skates on now don't they?