Travel London

The London bus operation of the National Express Group Travel London came into existence in its current guise when National Express bought out Connex Bus (established in UK in 1996, a division of French owned transport corporation Connex) in 2004. Ironically had taken over an existing operator Limebourne Buses which had actually taken over the original Travel London when it was originally sold.
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Are you speaking of just

Are you speaking of just regular buses, coaches or the double decker kind?

It is more a coach company

It is more a coach company than a real bus service, if it came from or through National Express. This means that they likely don't run many, if any routes off season, but in peak season they would be a nice alternative to the huge cost of city travel in London.