What is the maximum size of wheelchair or scooter that I can travel with on a train?

In line with the National Rail Conditions of Travel (Point 23.4), a wheelchair or mobility scooter must not exceed the following dimensions when travelling with Chiltern Railways.

The maximum Width is 700mm or 70cm.
The maximum Length is 1200mm or 120cm.
The maximum combined weight of the wheelchair and the passenger must not exceed 300kg.