Taps and check valves - I'm confused

My understanding is that if you fit a single flow mixer tap (kitchen or bathroom), i.e. where the water is mixed in the tap, then you have to fit single check valves (non-return valves) on both the hot and cold supplies (in addition to service valves). The check valve on the cold side prevents contamination of the cold supply and, on the hot side, it prevents cold water at a higher pressure being forced down the hot supply pipe. Fair enough.

If this is the case, then

1. Why don't tap sellers make it clear on their sites whether a tap is single or dual flow? Several of them point out that if you fit single flow taps then you must fit single check valves but they don't point out which taps are which.
2. Why don't people like Hep2O or Speedfit supply single check valves? Their catalogues only list double check valves.

I am currently trying to plan the plumbing for my new house and, either I'm missing something (more than possible!) or it seems that nobody seems to bother to obey the rules.

Can anybody sort out my confusion?

If you buy continental rubbish, you can be sure it doesn't have a CE or BS mark, (old Kite mark)

Speedfit do doublecheck valves

You can buy single or double check valves in compresion, which is suitable or plastic plumbers.

It's never a good plan to have different pressures, on a non-compliant mixer as the cold will prevent the hot from running.

Thanks doitall. What's the relevance of the CE or BS mark?

I assume that check valves reduce the flow a bit and that double check valves reduce it even more and so it's better to use single check valves rather than doubles. (I realise that there are some situations, e.g. outside taps, where a double check valve is compulsory).

Anything made in this country has to have a British Standard approved mark to comply with the water regs, particularly to prevent back flow, a BS approved mixer tap, mixes in the spout and not the body, if you notice the hot come out the middle, and the cold the outside, this also prevents scalding.

To appease our european partners because 99.9% of their rubbish doesn't comply, we changed the regs to a CE mark and you have to fit check valves.

All new install mixer taps have to be fitted with a blender to control the temperature, which also has a check valve built in.

Don't forget if you fit a mains pressure check valve to gravity hot then it won't have enough force to even open the spring, so zero flow.

To combat this BES do low pressure swing valves for gravity feeds, get the 1/2" BSP ones (female thread) and get some 1/2" x 15mm BSP connectors to convert to compression. They are a bit bulky but do the job.