We get a lot of enquiries from people asking if we hold passenger list records for people leaving and entering the UK. Just seen that findmypast.com in association with the National Archives have made available the passenger lists for people who left the UK between 1890 and 1960 (actually, they just got up to 1929 for now - the rest follows in the next few months and you can register to be kept informed).
While I'm here, Karen in archives recommends the 'Watching the Boats Go By' website. It shows live vessel movements in the Mersey and other areas around the coast, so you can check out what's afloat at any time of the day. You can click on the map to see the individual ships, their stats, what sort of vessels they are, where they're from/going etc and photos. Its great if you have seen a ship in the river and wondered what it was.