Brian,
Those generalisations are made for safety's sake and refer to grey imports.
You can add Puresound to your list of safe valve amps imported from China (and through a UK dealer network.)
The grey imports are not to be ruled out, they just need to be looked at by an engineer in the UK before they are even switched on.
Diy hifi supply looks excellent btw, however I have just checked their section on diy building advice. The equipment is configured for 115/230 volts. For the UK they need to be good for 253 Volts.
If in doubt about this contact Anthony Matthews at tubedistinctions.co.uk who has modified and made safe a number of Chinese-sourced valve amplifiers.