I don't know if anyone has been in the same situation as me and put off replacing the capaictors on the ECU, and then finally did so, but still had problems with lumpy running?

Anyway, I would just find it physically impossible to spend £50-£60 on a relay that was worth no more than a fiver (honest, it's rubbish really - £60 can buy you a 25kv vacuum relay that looks like a work of art), so I just pulled it out and resoldered all the joints on the PCB and I've got to say that this has made more difference to my car's performance than anything else I've ever done. It took sixty seconds to do (apart from prising all the panels off to get to it, of course), but the difference has been absolutely phenomenal.

I should say:

a. I'm not entirely sure there aren't some thermal fuses on the PCB. There's something there. They're probably diodes, but I soldered as quick as I could.
b. There are what looked like open bobbins within the main enclosure. I think drilling holes in the case for ventilation could cause gumming up of the works in the long run. The case is there as a dust shield as much as a physical enclosure.
c. It must get hot in there. On driving quite a way three days after resoldering I could distinctly smell the flux from my solder within the body of the car!

But, what I want to say is: If you're taking the ECU out to replace the capacitors (or for any other reason, particularly if it involves a soldering iron) just run a soldering iron over all the joints in the fuel pump relay. I know some are apparently more susceptible to dry joints than others, but there aren't that many to do anyway, and it's very hard to categorically spot a dry joint.