As far as the sound goes, Britpop artists have pulled influences from psychedelia, shoegaze, punk, and mod leanings; which are then best served by being showered in cocaine, wrapped in a Union Jack banner, and served atop an inverted picture of The Queen.

I think the thing that makes Britpop, Britpop is the direct, repeated mention and celebration of very British themes and places (Camden, Sheffield, Colchester, Manchester), regional accents, and the working class. Let me see if I can think of some relevant lyrics:

There's panic at London, Heathrow, everybody wants to go up into the blue, but there's a ten year queue. Blur, He Thought of Cars.

Bank Holiday comes six times a year! Day off from work to which everyone cheers! Bank Holiday comes with a six pack of beer, then it's back to work A-G-A-I-N! Blur, Bank Holiday.

If you could make an order, could you get me one? Two sugars would be great, 'cos I'm fading fast, and it's nearly dawn. Pulp, Bar Italia.

Just behind the station, before you reach the traffic island, a river runs thru' a concrete channel. I took you there once; I think it was after the Leadmill. Pulp, Wickerman.

We want your homes, we want your lives, we want the things you won't allow us; we won't use guns, we won't use bombs, we'll use the one thing we've got more of - that's our minds. Pulp, Mis-Shapes

As stated by IMOM, Britpop was a reaction against grunge and America.

Also: Manic Street Preachers

In conclusion, this.