Sorry Shaggy, I failed to read your initial post properly. If you're looking for 30metres plus on tug size, then you could give Svitzer (http://www.svitzer.co.uk/
) a call. They have fairly hefty tugs, scattered around the uk including down this way - their newer tugs are superb craft.
For barges and workboats, your best bet would be to get hold of Williams Shipping... they have barges, workboats, small tugs etc... and would probably be able to help you out on all the stuff you asked about in your original post. Goto http://www.wmps.co.uk/
to see what they're about - wmps is Williams Marine and Port Services, their local base in Pembrokeshire. They have some good little Damen stantugs, as well as other various craft for different purposes.
I could ask our lot for a day rate on a tug, but the cost I'd get could be completely different to what they'd say when they know what the job is.... it may be easier to just ask the people directly for a cost I think.