After all the advice in response to my earlier post "Router" I bought the
1/2" JCB 1200W from Argos. That's the Power Master model, rather than the
basic)

Good move !!

Three collets supplied, 6.35mm, 8mm, and 12.7mm(1/2") together with 5
plain shank 1/2" diameter bits.

Although fairly competent with most tools my router experience is limited
to one weekend with a hire tool so today I took time to RTFM and then
have a practice. Had a tough time getting the bit into the collet and had
to prise open the jaws a little to get it started. Instructions state
"ensure that at least 3/4 of the shank is held by the collet". That
needed some serious tapping with a blunt instrument just to get half the
shank in and these items are on the bench not in the machine, and by now
it's obvious that all is not well. To my unpracticed eye the shank looks
bigger than the collet sleeve so it's time for some measurement with
callipers.

Shank 12.7mm - Collet interior 12mm tight.

Obviously remedial action is required and will be taken ASAP but I am
puzzled by the collet size. Is 12mm a foreign size or a badly machined
size? The two smaller collets measure correctly.

Driving back into the city, with petrol, ferry fare, and parking, will
cost me about £8 and a 2 hour round trip so I'm planning to call a couple
of more local merchants first to see whether they can supply a
replacement.

Buying cheap (£60) isn't always a good idea is it?

--
Mike