I have a VW T5 transporter which has starting issues and have been advised that the ECU may be the culprit. Will a second hand unit be a direct replacement if it carries the same code number or will I need to have it matched to my van ??

It'll need matching to your van.

It is the least likely component to fail though.

ITBs and Omex 600, this is Locostbuilders after all ;-)

Get Vagcom,VCDS or a stand alone reader on it. VW ECU's are pretty robust unless they've been hardware chipped.

I know what the code is for the problem, issue is I cant find the problem been suggested that it could be the ECU

Probably coded to the vehicle.

Try giving BBA-reman a ring. They're usually pretty helpful. There's a note in their latest info sheet about Bosch ECU used on VW tdi's giving non-start faults. They'll collect, test, repair (if neded/possible) and return yours without losing the coding.