Thank you so much!

The answer was;

=IFERROR(LOOKUP(2,1/($B3=Sheet2!$A$2:$A$300)/(C$2=Sheet2!$K$2:$K$300),Sheet2!$L$2:$L$300),"")

Now just to find out what to do when there is 2 things booked in to a room.

I think that might be a problem for another day however!