I am planning to travel to Paris would i need a passport if travelling by train? ?

yes, you always need a passport to go into another country. No matter how you get there.

Yes

nope you want just a ticket

Yeahh
Because Other Wise Illegals Could Get Over Here For Nothing Practically
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Yes, if you are travelling outside of your country you will always need a passport, no matter what method of travel you are using.

Yes you need a passport to enter a country outside of the UK

not if your in france already

yes, a passport will be needed unless you hide in a box!

Yes, they'll check at the gate in St Pancras. If you don't have a passport I'd suggest getting one soon, there can often be a wait for them to send it to you (though when I realised I'd lost my passport a day before I was due to travel they did a 1-day service for £120)...check out http://www.ips.gov.uk/passport/index.asp for an online form and information for your nearest office.