5dn Mike and Robert were working on line in beer plant (12). Answer: MICROBREWERY - but is MIC an acceptable synonym for MIKE?
8dn Last couple avoid vespers in any event (4,2). Answer: EVEN SO - evensong less the 'last couple' of letters. However, VESPERS and EVENSONG are not synonymous. They are quite distinct.
6dn 500 wearing track suits here? (10). Answer COURTHOUSE - but I've no idea why...
15ac Supply curry where there are no seats (8,4). Answer: STANDING ROOM - but I've no idea why...
19dn Bigot adrift touring Spain (6). EGOIST? If so, why?
25ac What broke Burton's heart? Scotch (6). WHISKY? If so why?
27ac Current tip of warp is fed in to fix loom (6). _M____
16dn Mollify small child holding a gun (8) MITIGATE? If so why?
17dn A good place to see art in 11 in a state. (8) _G_______ (N.B. The answer to 11 is 'Identity Card')
Thanks to all who took the trouble to provide answers. I'm glad I didn't persevere any further with this as it would only have made me even grumpier. I must remember to avoid Redshank in future.
P.S. I'd still be interested to know the explanation to 19dn.