Betfair if you put money in the UK.

It's not. It's right next to the 'buy/long' field/dropdown for most online brokers.

The broker might make you jump through a trivial hoop to get a margin account and fax in an additional agreement. Stock short account you just had to request and to get option shorting my broker, TD Waterhouse, had a simple Q&A quiz to make sure you understood the risk profiles of option shorting.

Instead of short selling an equity (which is indeed complicated not so much in its difficulty but in its potentially unlimited downside), you can buy a put option. For the cost of the option you receive the right (not the obligation) to sell a stock at a specified price. If the stock price then goes down below that that price, simply buy the stock at the lower market price then use your put option to sell it at the higher price. The downside is limited to the cost of the option.