We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Dave Plowman (News)"
saying something like:

We reckon that the rates are fixed if employed, but are generally
being kept down due to Polish / Latvian imigrants. is there any truth
in that.

No. There are no fixed rates for any employment and skill - apart from
possibly in local government, etc. But few councils have staff in this
sort of area anymore - they use contractors.

If self employed you can try and charge what you want. But may not get any
work. Market forces. Nothing to do with immigrants. Just supply and demand.

Which is exactly the OP's point. In many parts of the British Isles
where there is an influx of Polish/Latvian/etc workers, rates are indeed
lower than they should be. Those lads, while nice enough fellows, will
work for half what a local will.

Employers love them for that, unsurprisingly. I expect the situation
will rectify eventually, but might take a couple of years yet.
--

Dave