The result is £925 a day for me, which in east midlands UK is a very tasty morsel.
In summary I'm a SaaS guy, being used to replace 3 Europeans who aren't likely to be there long-term to continue to build the product beyond its initial launch. My (albeit extortionate) day rate is less than their 3 combined, so it made sense for the company. Right place right time for me.
For colour, from your perspective: if you can get £500 a day in London that's not bad at all, up here in the East Midlands (I'm near Nottingham) I can get £350 to £400 a day, though I would normally trade some back for work flexibility (I prefer to work less than 8 hours a day).
Then wait a couple of days for the Recruiters' automated search systems to index your CV. You'll start getting phone calls about positions soon after.