There are 2 East London donut suppliers which are in a separate league. To give some background, I detest donuts in general - too stodgy, too sweet, and leave me feeling a bit sick. Then I tried a donut at a farmers' market a friend has set up, and I was hooked.
The better of the 2 is Bread Ahead. If you watched the recent Tom Kerridge series, one of the programmes featured Bread Ahead's donuts, which are sold at the Borough Market. Their custard donuts a pillow light with a smooth, light, and flavoursome custard. He does vanilla custard, chocolate custard, and praline custard, as well as other flavours. The baker is Justin Gellatly - ex head of St. John's Bakery, where he perfected the original IT donut. The problem is that they are administratively difficult to work with (need better admin support). As I needed someone to be reliable, I used St. John's Bakery. They are located in Bermondsey, but have an outpost near the Restaurant (they are the bakery arm to St. John's Restaurant). Their donuts, are a very close second to Justin's new venture. The difference in their custard donut, as per DS, is that it is more creamy than the Bread Ahead, which is more custardy. Do try both, but I warn you - the Bread Ahead one's are highly addictive.