PankySmooch: They use taxi's (or what look like taxis) a lot because they don't look out of place just pulled up by the side of the road. Decorators vans are also a good one because they just part them up and leave them (in the back is a camera which points out the back windows).
When they did the drug op outside my house they parked the decorators van on the lane. I had to ring the police and tell them to shift it because it was blocking the lane for other vehicles. About 10 minutes later this scruffy looking bloke in overalls turned (whilst eating a sandwich) up and shifted it. He was a plain clothed officer but you'd of never known! I was rather impressed because he just went "Alright mate" and moved the van onto the road side.
When the car arrived, 3 taxis just piled up on it and the plain clothed officers jumped out and arrested the driver.