I can't recommend NCT Nearly New Sales enough. If you have one in your area, they can be an amazing source of affordable baby stuff.
http://www.nct.org.uk/in-your-area/nearly-new-sales can tell you if/when one is coming up near you.
Also, if you've got an IKEA, you must check them out as well. We got our cot at the NNS, then bought the mattress at IKEA. Fitted crib sheets were also very cheap there. They also sell a stack of 10 washclothes for like 3 quid, and we've found those to be incredibly useful. It's definitely worth checking out what they have available before buying anything at a Mothercare/ Babies R Expensive place. Many of my friends have ended up with the standard IKEA highchair, for example, as it's apparently very easy to clean, and doesn't take up nearly the space that the other ones do. (we've ended up with a seat that attaches to the table- like the ones they have at Wagamama for babies. We bought a secondhand highchair at a NNS but have barely used it, and will likely sell it at the next NNS for about the same price we bought it for...)
And yes, Freecycle is awesome. It's been changed to "Freegle" in our area, in an attempt to distance themselves from the US version. (just fyi, in case you haven't found Freecycle where you area, it might be under that name now?)