Hi Woppy,
All extra leg room seats with Virgin are allocated in the same way as their exit seats, which are sold as one of the types of extra leg room seats. Exit seats must be allocated at check in because of the restrictions, for example age and mobility, attached to this type of seat.
Non extra leg room seats can be allocated online because they are not similarly restricted. I'm sorry that we weren't able to help you with this, but please do contact us if we can be of any further assistance.
Jo, Jetsave Customer Services.