The fact of the matter is that the UK CAP413 Radiotelephony Manual and the UK MATS Part 1 used to specify that it should be transmitted as "one thousand (millibars)". Then, a few years ago (four or five?), it changed to come into line with ICAO and it is now implied that this particular value should also be pronounced in individual digits, viz "one zero zero zero (millibars)".
I wrote to CHIRP many months ago on this subject as I thought that the original UK practice was very sensible insofar as it guarded against the possible confusion of 1000 and 1010. I seem to recall that CHIRP sympathised and forwarded it to CAA SRG - and a resounding silence ever since. I would have thought that this was a safety-related issue to which they ought to apply a little more urgency.
You cannot blame the ATC colleges for teaching to the book but I do wish that they would be more proactive in flagging up such problems to CAA - they ought to be the first line of defence on procedures such as this. Mind you, how many controllers or operational units have bothered to go into writing to CAA on such matters? All the effort in typing on an internet forum could be directed to better effect!