Yep, Hemswell is very similar to Scampton, Hangars and layout-wise. I wouldn't be surprised if they did do some filming there - it was much later that Hemswell became a Thor base.
I do know that the sequence shots of the Lancs taking off in 3 ship formation was done at Coningsby (it was the only place they could find that had a long enought stretch of grass without any giveaway concrete in the background (Scampton was a grass field when the raid took place).
The scenes - supposedly at Reculver - where they watched the tests (failing) were done on the sand dunes at the Wainfleet bombing range (Just outside Skegness)
The scenes of the crews going into the briefing was most definitely the Scampton airmen's mess - Hemswell wasn't that much of a Scampton twin. The final scene shows Gibson and Wallis just a few steps up the road from the Scampton airmen's mess entrance - alongside SHQ. -Again definitely Scampton.
There were two scenes I wondered about. One was where the Lancs are being delivered and you see them taxiing up the peritrack past a large black hangar - There was such a hangar at Scampton - it was taken over and used by MT as a garage - but the topography seemed wrong - Around there Scampton is almost as flat as a billiard board and there seemed to be rising ground around that hangar in the film. Then there were the scenes of the crews waiting for transport out to the aircraft. I suppose it could have been shot outside the Scampton hangars, but something felt wrong about it - couldn't put my finger on it, just didn't have a familiar feel to it.