Just a note if booking a Megabus coach fare in the UK- quite a few of their services are really local bus routes, not coaches, which are 'code shares' with Stagecoach- the local bus operator, and so not even operated in Megabus blue livery.
Check very closely for the clues in the route description on their website.
In that case it pays to check if the local bus fare is cheaper, especially with the current government bus fares cap. The bus should be in the Stagecoach yellow inter-urban livery.
Next week I am travelling from Reading to Cumbria via Oxford and Milton Keynes. The Oxford to Milton Keynes section is on the local bus route X5- turn up on the day and I will pay £2 on the bus.
Yet Megabus charge £7.20 + £1 booking fee for the same journey (and National Express, who also codeshare the journey) charge £6.40.
The bus continues on to Bedford- the on the day bus fare from Oxford is £2, Megabus charge £9.60 and National Express charge £10.
The reason for taking the odd route is that (apart from seeing the scenery) I then pick up an Avanti train from Milton Keynes to Cumbria (a 300 mile journey) for £12.20- an utter bargain.