On the subject of conversion, there are currently three jobs in central London. The salaries are 58000, 59331, and 70000. 59331 USD is 40999.97 GBP at the moment, so that's someone earning £41k who's converted properly. The others are round numbers, which suggests to me that they're in GBP and haven't been converted.

Not sure what to make of the fact that it's the two people with the highest salaries who didn't read the instructions.

It's definitely not a normal salary for a developer regardless of experience, even as a mid range manager (say managing a team of 20+) it'd probably be on the higher end.

Most likely a contractor, or adding on other considerations like stock grants; when I was at Salesforce.com they gave the stuff away like candy, so while my base salary wasn't too great the full compensation was good.

Yes, that's about right from my position of working as a contractor in London.

A fair amount of that is then paid out by the contractor's company in annual corporation tax and a little more in PAYE/NI.

As a contractor, you'd be looking to keep about 70% to 80% of what you invoice depending on how much you take in salary vs dividends.