Handshakes, hugs and cheek kisses
What it really means
First meetings usually get a handshake (work) or just a smile and "Hi, nice to meet you" (casual). Hugs are for friends; one cheek kiss happens between some friends, mostly women or mixed pairs — but many Brits don't kiss at all. Physical greetings are lighter here than in much of Europe. When unsure, a smile and hello is never wrong.
Context, tips & common mistakes
The British greeting repertoire, in ascending intimacy: the nod-and-'alright' (strangers you pass repeatedly, e.g. neighbours), the verbal-only 'hiya / you alright?' (most daily encounters — note no handshake), the handshake (first introductions, anything professional), the one-armed hug or full hug (established friends), and the single cheek kiss (friends, more common in the South and among women). Two kisses reads continental; nobody minds, but nobody expects it.
The famous awkward hover — two people simultaneously unsure whether this is a handshake, hug or kiss occasion — is universal and laughed about; the resolution is to commit early to one gesture or simply mirror. Note that Brits often greet without names ('alright mate!' from someone who has known you two years) — not forgetfulness or coldness, just the local register. Your name will be used when it matters.