You can travel on one bus directly all the way between Dublin and London or between Belfast and London or between Belfast and Glasgow (you can also get on/off at various stops in Britain along the way).  If you do this, you book through a bus company. While on the ferry you can use all the normal ferry services.  It means you don’t have to figure out connections etc as you are with one company all the way through.  It is normally cheaper than other ways of travel too.

Bus Route	Run by	Ferry route on way	Frequency
Dublin – London	Expressway Eurolines www.expressway.ie/eurolines  UK National Express www.nationalexpress.com/	Holyhead- Dublin	Once or twice per week in each direction, departing in the evening and arriving next morning, about 12 hours.  At time of writing it was running Dublin to London Friday evening to Saturday morning, and from London to Dublin Saturday evening to Sunday morning.
Belfast – London	Service run by www.translink.co.uk (aka Ulster Bus) also bookable through UK National Express www.nationalexpress.com	Cairnryan- Belfast	Once every day in each direction – leaving London early morning arriving Belfast mid afternoon, leaving Belfast mid afternoon and arriving to London early next morning.
Belfast – Glasgow	hannoncoach.com Service run joinly by www.translink.co.uk (aka Ulster Bus) and www.citylink.co.uk, also bookable through UK National Express www.nationalexpress.com	Cairnryan- Belfast	Multiple times a day in each direction

Bus-on-ferry and luggage

Bus-on-ferry: For some services, such as the Belfast-Glasgow service by Hannon Coach, the bus crosses on the ferry, and you can choose to leave some luggage on the bus.

Bus-on-each-end: For other services, such as the Belfast-Glasgow service and Belfast-London services by translink/Ulsterbus/citylink/national express, the bus doesn’t travel on the ferry, rather one bus brings you to the ferry on one end and another bus picks you up from the ferry at the other end. This involves collecting any luggage you have and checking it in again when transitioning from bus to ferry, and from ferry to bus.

See also our page on bringing a bike on these buses.