Spike speak is almost exactly like normal Angel speak (e.g. he doesn't use Buffy/Willow slang) with a few English words thrown in. He's not a cockney, but a North Londoner, which makes all the world a difference.
General words he uses:
For emphasis: bloody, soddin', effin', frickin/friggin (where we would say "I can't believe you'd do a thing that!" He'd say "I can't believe you'd do a bloody thing like that!") Warning: don't put too many in. It's only for emphasis. Kinda like our saying "fuck" or "fucking" in our sentences before certain words.He'd always use bollocks or knackers for testicles
Telling someone to get lost or how we would say "fuck you": piss off, bugger off, sod off
When we'd say 'oh god' because the world is about to end, he'd say 'bloody hell' or 'bugger.'
Poof is a derogatory term for a homosexual male. So is 'nancyboy' or 'trotter'
Pillock, wanker, tosser, ponce, nonce are all general 'you are an asshole' terms for males
Peaches, pet, luv, ducks, sweets... are used in general conversation in place of someone's name. Not really used because of affection for that person.Bloke is used when the speaker doesn't know the person personally
Shag, get a leg over, give a good seein' too, all mean to...if you don't know this by now...
cow, dozy mare, bint, twat are all derogatory terms for females (like our bitch, whore, although he'd use those terms, too)
"She's gagging for it" = derogatory, i.e. she's so horny she'd do anything to get laid.
In general, you just want to pepper Spike's speaking with a few British words, not overload the piece. North London English is very close to American with a little bit of slang thrown in.