Financial assistance to opposition parties, known as Short Money, is governed by the resolution of the House of Commons of 26 May 1999, in which the purpose of the payments is described as being
“to assist an opposition party in carrying out its parliamentary business.”
The resolution provides specifically for funds to opposition parties for travelling and associated expenses necessarily incurred by party spokesmen in relation to the party's parliamentary business. In addition, assistance is available for costs necessarily incurred in running the office of the Leader of the Opposition.
There are no restrictions or rules on the mode of travel that can be used in carrying out parliamentary business.