In Australia there is a fantastic bag/satchel/backpack etc company called Crumpler which is highly favoured by uni students. Not sure if you can access them in the UK but they make really great large/medium satchels etc that I think would really suit you. I received a Crumpler backpack for Christmas from my DH. There's a piccy of it in my gallery. Love it. Asked for a backpack because with kids in tow you often need hands-free. They are also extremely well made. There's a also a BB thread about them... do a search on "Crumpler" if you are interested.