We do, but because the ASA is specifically excluded from oversight of political advertising, I think this actually causes problems in the UK. There's a general understanding that "if it wasn't true, they wouldn't be allowed to say it" which is fair enough most of the time but means that political advertising either online, in print, or on billboards, etc. can get away with - essentially - lying, without any consequences whatsoever.
The ASA did used to police political advertising as well, but that was taken away from it on the understandable basis that it was unable to respond in a timely enough manner to the kind of advertising used in the short timeframe of, say, an election campaign. The power was taken away on the basis that a new body would be set up which was specifically designed to respond quickly. Fair enough, except the new body was set up so now... nobody regulates political advertising.