A mate of mine managed to do this and him, myself, and a few of his friends all made a few bob out of it (£300 a month ish).
It involved him writing a small app that ran on virutal servers on the web. It hooked up to bet 365 (which has a well documented API) on one side, and automated the ladbrokes website on the other to do the match betting. It worked because...
a) 365 don't really limit you because they make money out of every bet that happens even if you are a winner or a losser.
b) the ladbrokes site was slow to update its odds and thus you had more of a chance of finding a matched bet via them.
Its downfalls...
a) Ladbrokes would limit your account after a while and thus would stop you from putting big bets on and thus make more money. In the end the accounts on ladbrokes where getting more and more restricted so that we could only put something like £10 bets on.
b) If labrokes changed their site design, the software would then fail.
In the end, Ladbrokes managed to change how the system worked by changing their site and basically it wasnt going to work via them anymore, so we closed it all down.
This all happened last year, and I just so happen to be meeting up with him tonight, so I am thinking I will egg him on to try and find a new site we can work with
Could do with the extra quid.
When I think back to the whole run of the software, I am quite pee'd off that we initially put limits on the size of the bets we would do with ladbrokes to hide the whole thing because we thought that they would cap the account faster. In some of the late comers to the scheme, we decided to up the limits a lot, and they made some quite large winnings over the months.