A PUC or a Pollution Under Control Certificate is usually required for vehicles which are older than 3 months on the road. You can easily get one in a petrol station in Delhi (or in other metro cities of India) in around 40 INR. The certificate is valid for three months and involves a quick 5 minutes check up.

Here is my certificate (which is expired though!):



You can probably get one done at a gas station even on a UK registered bike. The PUC though necessary, should not prove to be a deterrent even if you dont acquire it. Such is the leniency of this country. In extreme cases be ready to shell out a hundred bucks as 'ignorance' fee to the law enforcement officer.