im just going on the fact he has detected a 3 amp draw with everything off, even though it is intermittent.
plus the battery appears to be draining overnight rather than just after a journey...to me that would eliminate the alternator, which the diagnosis doesnt really make sense to me
Yes, but the question is, is it in to the alternator, as seems to be suggested by the Garage, who has looked at it, or is it somewhere else. Now, the problem is that the garage's description of their diagnosis seems a bit implausible, so we really don't know.
Now, if it is going somewhere else, there is no case for doing anything with the alternator. You could take the belt off the alternator and slowly rotate the alternator and look for a point at which you get the current drain, that would be a way of testing whether the garage's diagnosis, as stated, is correct (but I suspect that they've just 'dumbed down' their diagnosis for you and they've really mis-described or oversimplified it, but that's just my suspicion).
(I would say, don't try to spin it fast and look for the charge - we know that it is charging some of the time, anyway, and you'd have to get the alternator up to 1500 - 2000 rpm to really get it working, and for that you need a drill and a pulley, and, unless you can look at the current waveform you'll probably not learn what you want to know.)
The breakdown of the price is £150.00 Alternator & £75.00 labour, I like to think that I am pretty smart, but I didn't think of buying a recon/2nd hand alternator as an alternative. Could I ask the garage to fit it for me? I have seen them on ebay for circa £30.00 is it worth this as an option?
Personally, I'm not a big enthusiast for the 'Bay of Fleas', but a more co-operative Garage might have mentioned the possibility of getting a remanufactured alternator, for which yours is usually taken in exchange, and there may be a deposit to be paid until they have yours. From a scrappie is probably cheaper, but with less of a Warranty. A Motor Factor ought to be cheaper than a Ford-branded one, by some way. The Garage hasn't really, as I understand it, said that you'd be getting a Ford-branded one, anyway, so at least check what you are getting for the money, which seems on the high side.
My preferences, assuming that some test does conclusively point the finger at the alternator, would be Motor Factor or Remanufactured/Reconditioned, but if a scrappie is way cheaper, that could persuade me. YMMV.
The £75 labour doesn't sound too unreasonable (a bit high, but not excessively so), but the garage hasn't helped you much towards the economical options, and you might have expected them to query what you wanted, on an older motor. And what if it isn't the alternator? Do they take responsibility if they've got the diagnosis wrong (ie, you don't have to pay, or only pay once and they fix it, whatever the cause actually turns out to be)?