I can't think why you would want to darken your pudding; surely it's the taste that matters, isn't it?
However 'browning' is/was exactly the same stuff as 'gravy browning' , which is still available (under the Sarson's brand name) in Asda (84p), Tesco (85p), Morrison's (85p), Waitrose (89p) and Sainsbury's (£1.00).