Dulux Decorating Centres sell their trade paint, but are open to the public. I was told today that they are having a 25% off everything weekend on 16-18th October.
The paint is thicker than DIY paint, and I'm told that you can often use just one coat. A 5L tin of magnolia is £27.
They mix bespoke colours and sell in 1L, 2.5L and 5L tins. I bought a couple of samples, and was surprised to get an actual tin which was quite big - 250ML for £3.69. If you decide to buy the a full tin, they will refund the price of the tester, and also give the 25% off for the special weekend!
The Edinburgh staff were super friendly and helpful and I was very impressed as I'm a total DIY rookie
They accept nector points also.
I hope this might help some people who are decorating in the next few weeks