In reply to Cory Ander.
I have to admit on my first batch I just used knorr stock cubes as I didn't really think it would make a difference. I was reticent to use any stock cube/paste at all as I know from experience that it hinders the oil removal process later, but to try to keep to the recipe I used what I could get hold of at the time.
However, I've since made another batch because I managed to get the knorr paste and there's a good tip here. I asked my mates to ask at their works' canteens to see if any of them used it and it turns out that two of them did and so I managed - or rather my mate managed - to scrounge a small cup full for me. The only thing is that I didn't realise that there were several varieties of the paste and so I'm still not sure if I used the exact same one as CP recommends. However, I think it's academic because, as I expected, it made no perceptible difference to the flavour of the base as compared to the plain stock cubes.
If you want to buy some just Google "Knorr vegetable paste". I found five different catering suppliers within a minute. It's expensive though, cheapest was about ?12 per 1kg tin.
YF
P.S. If this really is a common ingredient of high street curries it will be available in quantity at any asian grocer/spice merchant.