Where in the country are you? That would help us to recommend. I can recommend 4 places :-D
I don't think a fertility test is a waste of time. My oldest boy sired some litters, then mated twice with no pups, so that obviously sent alarm bells ringing. On testing we found he had become sterile for reasons I'm not going to go into here. So I bought one of his sons to take over his father's duty - the line of breeding had been many years in the planning. This first time around I had him tested at Fit and Fertile then went to Croft in Newcastle for all the tests only veterinary specialists could do - the important thing was to check that he was fully fit and healthy.
I double checked he was still as he was at the beginning of last year, sadly he was still infertile. However, I am extremely relieved that I did have him tested as it highlighted a health issue. He was tested at Fit and Fertile, Preston. Keith is NOT a vet, however, he could tell me that all wasn't quite as it should be, so I instantly drove straight to my vet. Turned out to be a prostate problem, all now fully sorted. Had I not have taken him for fertility testing I may not have known about this until it had become a lot more serious. So, yes, I would say it's worth spending money to get him checked over. Someone's already said, Fit & Fertile were around £40, if you go to fertility specialists it will be considerably more ... the first time around I did that as I was concerned there may be bigger underlying health issues.
The specialists I went to were Croft Vets in Newcastle who were excellent
http://www.croft-reproduction.co.uk/.
The others I'd recommend - Susan Long, can't for the life of me remember off hand her practice, just outside Bristol, but she was/is on staff at Bristol Uni - didn't see but had many communications with (fortunately a friend of a friend) but I've an inkling Brainless may know of her ... hope she pops on!
Also Angelika von Helmendahl at
http://www.vetrepro.co.uk/ in Cambridge came highly recommended by someone else who has needed to see her.
Hope this all helps.
If you go the testing route, it is so much easier if you can arrange a teaser bitch, I took one on each occasion ... sometimes it really is a case of asking around acquaintances and asking if you can borrow their girly for the day - I had to on one of the 3 occasions!! Took a bit of explaining :-D