Cleaner
My vote would be for a straight suction Eureka, by the shape of the top of the bag. It was certainly not a Hoover as the bag was across the front of the handle, and indeed looking at a 1928 article the Eureka is the only model with the bag in that position. It could not have been a Morphy Richards, the company did not exist then.
For those who have not seen it yet, the cleaner only appears for a few seconds in the opening scenes of episode 1, and you do not see the whole of the cleaner, just the handgrip and the top of the bag. The mixer comes later, although it is never made clear who actually authorised the purchase of the mixer - well not so far anyway.
Despite the Earl appearing to be something of a stick in the mud, it appears that they are quite forward thinking regarding domestic appliances with a toaster and now mixer and vacuum appearing for use by the servants but I suppose that would be due to his having an American wife.
It is almost certain that the running sound of both the cleaner and the mixer were added after the event and would not have been the actual sounds of the machines due to safety regulations noted above
Al