the latter... welcome to 1990s America, that is where it really took off - especially in the dot com boom - loads of people quitting their jobs to trade for a living when really they were riding a big up trend
the problem in the UK is we have a stamp duty tax on stock transactions for private investors, this makes intraday trading of stocks, directly, unfeasible compared to the US - they don't have stamp duty, their brokers offer margin accounts and facilitate stock borrowing so you can 'short' a stock (essentially you borrow some shares and sell them then later buy them back and return them - if the price has dropped then you make money). Basically as long as you've got $25k you can punt away on a proper exchange in the US.
In the UK there are spread betting firms, these sorts of firms used to exist in the US 100 years ago and were called 'bucket shops'(obviously they didn't have websites back then but ran on the same principle more or less) - they're now illegal over there for stocks, commodities etc.. but are fine here - they're deceptively expensive so not actually a good idea for frequent trading but will allow you to make use of margin/leverage and bet that a stock will go up or down. There are a lot of things wrong with these firms but that could take a whole wall of text to go through.
The other way to day trade stocks in the UK is via a CFD - contract for the difference - some firms offer these in basically the same way as spreadbets - so essentially pointless and mostly a rip off. Other firms give you direct market access to the LSE and elsewhere - you can dodge the stamp duty tax, trade with margin and go short... essentially just like retail traders of US stocks can.
Interactive brokers has a CFD offering and they're probably the best value.
Generally though, unless you've got a legitimate edge then intraday trading is just going to churn your account and cause you to lose money rather than gain the instant riches you're potentially hoping for.