Salaried Developer @ £40K £3,333.33 Gross £2,512.89 Net
Contract Developer @ £350 per/day using a trust £7350 Gross £6027 Net
Contract Developer @ £350 per/day using an umbrella £7350 Gross £4,333.68 Net
Contract Developer @ £350 using Ltd £8820 Gross using flat-tax scheme You'll need an accountant to tell you what you can actually get net, if you have a wife that doesn't work it'll closer to a trust, if you don't, it'll be closer to an umbrella, but you can defer to bring it closer to the trust if you're patient.
I'm not sure what people actually get paid in SV, but £350 is fairly low end, you can pull £600 a day in London which'll earn you $250,000 assuming you never take a holiday or are inbetween jobs, which isn't a good idea.
P.S. The salaried developer probably costs the company more too.
FYI you don't need to be in the UK to contract, I just don't know the tax structures elsewhere.