Can a 2×10 front mech be used on a triple crankset that is set up as a double and a bash?

Yes, the spacing of the rings is the same. The chainline is slightly different (1.3mm) than a true double crank, but there should be enough adjustability in the front mech to accommodate this.

Thankyou PerthMTB

Oh, one other thing to consider – if your bash is significantly larger diameter than your ‘big’ ring it may foul the FD cage. If so, you’ll need to set the FD a little higher than ideal (or get a smaller bash!)