Help Needed

[suprababy]

I bought a UK spec tt 1 couple of weeks ago, after a few days i turned the ignition and one in every 10 or so times it would just click then the next time or so it would fire up. After reading some threads i changed battery. The car started fine all that day and the following, the next time after that i started car and it just kept trying to turn over - i removed key from ignition and it was still trying to turn over - with no key in - so i put key ack in and it started but was still trying to turn (sounded like it anyway) whilst it was running - so i drove to the garage i use about 8 miles away and for most of that time the strange buzzing noise was there but cleared up before i got to garage - typical - the car turned off fine at garage and we tried starting it again several times and it was fine each time. So we think it could have been starter motor sticking or something so today i got it reconditiond from autolec - that was only £30 so i was pleased with that. But now the garage has put on the starter motor and its starting up fine but he said it is now overcharging about 16 or 17v - they think it could now be the alternator - what do you think - any suggestions please!