Lidl 10th Dec offers out

[Rorschach]

I was out shopping this morning so had a look at their bits. Picked up a pair of 300mm quick clamps for £6, they are ok, not the greatest and certainly not a patch on a g-clamp of anything but plenty good enough for a little bit of pressure when gluing/screwing/pinning or just to stop a board sliding around. Happy with them for the money.
Also picked up some angle grinder discs, they were 2 packs for £7 so I had a 4-pack of diamond discs and a 12-pack of cutting discs. The cutting discs are 125mm to fit their own grinder but I find thin discs like that will fit fine in my dewalt 115mm grinder.

Not a bad morning

[Job and Knock]

I wonder if they make Routers using ER collets, seems like a good idea to me, I love my ER40 set.

No, but some European-designed DW routers (e.g. DW624/DW625, etc) use engineering collets. WW collets are a lot smaller than most engineering collets which may be part of the reason.

[Job and Knock]

....given that 1/4" is 0.35mm's bigger than 6mm it would be tighter not looser, if you could get it in the collet at all that is.

If the collet is a good fit you won't be able to shove a 1/4in (6.35mm) shank into a 6mm collet, and that's that. If you could do that then the collet would need to deform to hold the rated 6mm collet

You can pick up those collet adapters for as little as £1 but I think I'd go for a Trend version that's £9.
Trouble is they all say 'not for prolonged or heavy use'.

Quite right, too. Better quality collets have a multi slot design (look at a DW625 or Festool OF2200 collet to see what I mean, or fgor that matter an ER-series engineering collet) whilst cheaper collets are a 2- or 3-slot design (i.e. most Japanese routers) with smaller collets on some laminate trimmers having just a single slot. The fewer the slots in a collet or adaptor the less pressure it can exert on the shank because you have fewer contact points through which power can be transmitted. Given that most collet adaptors are one, or at best two, slot items it is surely self-evident why a 1-slot adaptor in a 2- or 3-slot collet won't have the best grip on the cutter shank - and therefore why vendors should be stating 'not for prolonged or heavy use'