I live in London, have a tandem, don't have a car, have done many trips with it on train.
I tend to put it on and ask questions later, the below is based on experience.
Greater Anglia - fine
South Western Railway - fine
Thameslink - fine
Avanti West Coast - fine with a reservation
Great Western Highspeed Paddington - forget it
Great Western Lowspeed Paddington - fine
Scotrail - it depends
I live in London, have a tandem, don't have a car, have done many trips with it on train.
I tend to put it on and ask questions later, the below is based on experience.
Greater Anglia - fine
South Western Railway - fine
Thameslink - fine
Avanti West Coast - fine with a reservation
Great Western Highspeed Paddington - forget it
Great Western Lowspeed Paddington - fine
Scotrail - it depends