Vaude seem to do a good range, like the look of the Trail Lights - except they don't seem to have a loop for a light.

I shall check them out in Evans if possible.

I have been commuting with a Vaude rucksack for years. They make the Edinburgh Bicycle Revolution range as well - see http://www.edinburgh-bicycle.co.uk/catalogue/detail.cfm?ID=21865
I've been really happy with my Vaude - can get a laptop, sarnies, couple of books and a few other bits and pieces in the 25l version, and it's really stable on the back. BTW I can't help feeling it's the reflective trim that'll show up at night, rather than bright colours, and the ability to hang LEDs on your bag is useful as well.

If no joy with a hi-viz pack, have a look here
http://www.wildlifewatchingsupplies.co.uk

They do a cover in day-glo to which you can stitch reflective tape.

OK, at £25 in p&p it's not cheap, but what price visability?