My condensor looks pretty rough too, but the aircon still functions pretty well. It's only the cooling fins that are disappearing, the actual pipes that carry the gas look reasonably okay. As culzean says, don't go anywhere near is with a pressure washer, or you will lose some more of it.
I then started get up and the AC clutch kicked in briefly, freezing air from the vent with my hand in front of it but then the temp rose up to ambient (10c at the mo).
Sounds like it 's holding some gas, which is good news. As soon as the compressor starts, it's dropping the low side below the minimum pressure switch threshold. Probably not a leak, you get natural leakage of the gas past the seals in the pipework, particularly if the aircon is not used for a period, allowing the seals to dry out. For that reason, it's a good idea to run the aircon at least once a week, even in the winter, just to redistribute the oil throughout the system - this helps prevent leakage of the refrigerant. Eventually, however, all systems need regassing.
If you take it for a re-gas, they will do a vacuum test before refilling. It's not infallible, but it should find any significant leaks. Any of the more difficult slow leaks can usually be found after regassing, either with a sniffer tool or by putting a UV dye in the gas.