I don't envy you with this one.
Do you have any of his documentation such as pay book, discharge certificate, etc......? Or, does anybody else in the family have them, the Service Number should be on them. Unfortunately they didn't put these on the medals in WW2.
Have you tried under variants of his forename such as Bert, Bertie, etc.....? or, did he have a middle name? They may not automatically look for these in a search.
You could try posting a photograph and request in the British Legion Magazine, they do a contacts and looking for section.http://www.britishlegion.org.uk/about-u ... legionline
Or, the Royal Engineers Association (REA)http://www.reahq.org.uk/
Hope this helps