As Britain is an island, ferries were the only way to get into the country prior to the advent of aviation and later the construction of the Channel Tunnel which gave a "dry foot" route from Britain to the continent for the first time since the Ice Ages. See also the Get in section of the Britain article. Below is a list of routes that cross the North Sea, English Channel or Irish Sea. It may not be complete.

The modern Seven Sisters Ferry, Newhaven
Major airports and ferry routes (some are missing)

Portsmouth and Southampton act as ports for transport to the Isle of Wight; Portsmouth and Poole also have routes to Guernsey and Jersey, provided by Condor Ferries.

The Irish Ferries Ulysses, the world's largest ferry
From Mainland Europe and Ireland to Britain
Overseas portBritish portCrossing durationService patternCarriesOperator
Amsterdam-IJmuiden, The NetherlandsNewcastle (Tyne Corporation Quay)16 hours1 nightly🚢🚘🚲DFDS Seaways
Rotterdam-Europoort, The NetherlandsHull King George Dock10 hours1 nightly 🚢🚘🚲P&O Ferries
Zeebrugge, BelgiumHull King George Dock8 hoursService withdrawn.βˆ…P&O Ferries
the Hook of Holland (Hoek van Holland), The NetherlandsParkeston Quay Harwich International Port7 hoursThe "Hook Continental" route. 1 daily, 1 nightly🚢🚘🚲Stena Line
Dunkirk (Dunkerque), FranceDover Eastern Docks105 minutesEvery 2 hours, atop each even hour🚘🚲DFDS Seaways
Calais, FranceDover Eastern Docks90 minutesThe "Golden Arrow" route. Frequently, though irregularly, throughout each day🚢🚘🚲P&O Ferries
Calais, FranceDover Eastern Docks90 minutesThe "Golden Arrow" route. Frequently, though irregularly, throughout each day🚘🚲DFDS Seaways
Dieppe, FranceNewhaven Town4 hoursThe "Transmanche" route. In Summer, 2 daily & 1 nightly
In Winter, 2 daily northbound, 1 daily & 1 nightly southbound
🚢🚘🚲DFDS Seaways
Le Havre, FrancePortsmouth International Terminal6 hoursService suspended (as of Oct 2021)🚢🚘🚲LD Lines
Ouistreham (Caen), FrancePortsmouth International Terminal6 hours3 daily, 1 nightly🚘Brittany Ferries
Cherbourg, FrancePortsmouth International Terminal3 hoursService suspended (as of Oct 2021), normally 1 weekly, southbound Sunday nights / Monday mornings, northbound Monday nights / Tuesday mornings🚢🚘Brittany Ferries
Cherbourg, FrancePoole5 hours1 each morning southbound, 1 each evening northbound. Seasonal service, operates April–October only.🚢🚘Brittany Ferries
Saint Malo, FrancePortsmouth International Terminal11 hours (9 hours during day)4-6 per week, depending on season🚢🚘Brittany Ferries
Saint Malo, FrancePoole4.5 hoursNo information🚢🚘🚲Condor Ferries
Roscoff, FrancePlymouth6 hours2-6 per week, depending on season🚢🚘Brittany Ferries
Bilbao, SpainPortsmouth International Terminal36 hoursThe "Peninsular" route. 3 weekly🚘Brittany Ferries
Santander, SpainPlymouth24 hours2 weekly🚢🚘Brittany Ferries
Rosslare–Europort, IrelandPembroke Dock, Wales4 hours2 daily🚢🚘🚲Irish Ferries
Rosslare–Europort, IrelandFishguard, Wales2 hoursThe "Innisfallen" route. 2 daily eastbound, 1 daily & 1 nightly westbound🚢🚘🚲Stena Line
Dun Laoghaire, IrelandHolyhead, Wales2 hoursService withdrawn; the "Irish Mail" route no longer serves DΓΊn Laoghaire, & now docks at Dublin Port (see Dublin to Holyhead below)βˆ…Stena Line
Dublin Port, IrelandHolyhead, Wales2 hoursThe "Irish Mail" route. Every 6 hours. 🚢 not conveyed on certain late-night & early-morning sailings.🚢🚘🚲Stena Line
Dublin Port, IrelandHolyhead, Wales2 hoursThe "Irish Mail" route. Every 6 hours; additional sailings operate in the Summer. 🚢 not conveyed on certain late-night & early-morning sailings.🚢🚘🚲Irish Ferries
Belfast (Terminal 2), Northern IrelandLiverpool/Birkenhead, England8 hours1 daily, 1 nightly.🚢🚘🚲Stena Line
Larne, Northern IrelandFleetwood, England6 hoursNo information.βˆ…Stena Line
Belfast, Northern IrelandLoch Ryan (near Stranraer), Scotland2 hours6 daily. 🚢 not conveyed 23:00–06:00.🚢🚘🚲Stena Line
Larne, Northern IrelandCairnryan (near Stranraer), Scotland2 hoursThe "Northern Irishman" route. 7 daily🚢🚘🚲P&O Ferries
From Ireland and Britain to Mann (Douglas), all operated by the Isle of Man Steam Packet Co and conveying 🚢🚘🚲.
FromCrossing durationService pattern
Heysham (Lancaster), England3 hours 45 minutes2 daily
Liverpool, England2 hours 45 minutes1 each evening, April–October only.
Dublin, Ireland2 hours 55 minutesInfrequent and seasonal
Belfast, Northern Ireland2 hours 45 minutesInfrequent and seasonal

These routes may be subject to change. It is recommended to contact the ferry operators and book ahead.

By coach or bus

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If you are booked onto a scheduled international bus route that crosses the Channel, it may either go by ferry or through the Channel Tunnel; you don't get the choice. However, in general FlixBus uses the tunnel, Sindbad and Transmarian use the ferry, and Eurolines use both, depending on route. Schedules can change day-to-day depending on conditions at sea and fluctuations in ticket prices between the ferry companies and Eurotunnel. You can also catch a domestic bus to any Channel port of your choosing and take the ferry as a foot passenger, but this is not possible with the Eurotunnel. If you are going on a package coach holiday, the company will always explain how you are supposed to get to and from your start point.

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