A real long shot but my cousin has been let down with the villa in Mallorca they had booked, the owners have just cancelled the booking due to an "apparent" kitchen fire. Does anyone know of a villa available 12-24th August and has 4 bedrooms to sleep 8 people or any likely sites to look including Facebook pages I could go on? Thanks in advance.

That's a tall order. Most people book these things in November of previous year.

And it won't be cheap either.

AirBnb is probably your best shot. Also try this German site.
The Germans have a knack for securing the nicest villas for their holidays. And they are in the Euro, so they don't suffer as much gouging because sterling is so strong.

Good luck...

Yeah I know, they were just informed it was cancelled yesterday.
Thanks for the reply, I'll pass the info on.