Success! Got my new radiator in after 2 years of thinking about it. Took about 6 hours in the end including hangover faffing, and no small amount of butchery to get past a few areas of corrosion. Hopefully I'll now be able to cruise around with the aircon on, instead of the heater on full! If I get this right, there should be some photos attached showing the old radiator; about quarter of the radiator was completely gone with daylight in between, the remainder was pretty corroded. (To be fair, it was 9 years / 116K miles old
Also, for interest, the contents of the washer bottle in a bucket (I thought the headlamp washers had a check valve, if they have then mine doesn't work!!) I was amazed by how much fluid there is!