My local B & Q didn't have any trailers, Halfords do, YUCK and expensive!!
I didnt mention in my original post, I have looked at several second hand
trailers and although I consider myself handy with a welder etc, miricles
I'm not so good at, I can't weld rust.:-)

Ok, spent the day researching

Suspension units 500kg capacity
Hubs to fit Ford wheel (I have a ford mondeo, so wont need spare for the
trailer)
weld on plates for units
All from http://www.trailerpartswarehouse.co.uk
total cost £87

Went to my local Smithy

Angle iron, 50mm x 50mm x 5mm x 6 metres £12 (base)
30mm x 30mm x 5mm 6 x 12 metres £25 (top and to make hinged back door)
Box section, 50mm x 50mm x 5mm x 4 metres (for drawbar that goes all the way
to the back of the trailer and for the axle)
£56

Local scrappie wants £5 for a pair of Mondeo wheels with tyres

Already have tow hitch ( only salvagable thing from my old trailer)

Have welder, angle grinder, clamps lots of space and have been welding for
ten years (self tought) although I'm used to welding broken JCB diggers, RSJ
etc

I'm planing on floorboards for the floor and sides, would I be better of
with plywood? what will last longer?

So is this overkill? I want to be able to do 70 down the motorway loaded
with with 300 - 400 Kg's of whatever

Thanks for the input guys

Drew