Hunter - thanks for your input. In answer to your questions:-
1) I have had the car for 6 months but it was bought privately
2) It had done 31,000 miles when I picked it up and 35,000 miles when I took it to the garage for the first time
3) The car has been off the road for around 40 days in the last 3 months. Each time I have picked it up the problem has reared it's ugly again very quickly and it's gone back in
4) The car has been to the dealer 5 times and this 5th time they have had the car for 31 days and counting. The last time it went it I had a problem starting the car in the first place! Called the AA to get it towed to the garage and they had trouble starting it too
5) Each time my car has gone in I have received either a courtesy car or a hire car but one of the times I had to pay for insurance on their courtesy car! Also, during this current prolonged visit, ARUK said they would not extend the hire of the car I was in as I bought my car privately! I could not believe this and questioned it with the garage. They said that, unofficially, ARUK treat people differently when they have bought the car privately to when you have bought as an approved used car from a dealer when it comes to warranty issues and in particular the subsequent use of a hire car
6) I have been in touch with ARUK on a regular basis and they have been liaising with the garage too. There is a case open with them and Teseo have been assisting under that case ref.
7) I have a good knowledge and memory of the issue myself but I have been writing a lot of the details down too. I called the Government Consumer Helpline and they advised me to check the warranty to see if it specified a timeframe in which Alfa should fix any fault. If it was over this time (as I'm sure it would be by now) then I should demand a resolution within 14 days or a like-for-like replacement vehicle. I should put this in writing so this is my next step but I don't know what the warranty says.
Guest say they replaced a customer's engine once but this would be the very last resort. They also said they would definitely fix the issue, it's just a matter of time!
I had a 147 Selespeed a few years back as it was the worst nightmare car I ever had. I vowed never to have another Alfa. I then saw the 159 TI and my heart wanted one. I listened to it and got one. For 3 months everything was fine but now things are just as bad as when I had my 147! :-(