US Citizen / UK Permanent Resident - do I still file?

I'm a US citizen married to a Brit - I'm a permanent resident in the UK and have been working / paying taxes in the UK for the past 6 years.  As I live here permanently (have an NI number, pension, mortgage, etc etc) and work for a UK employer it never occurred to me that I have to file....do I?  Any advice much appreciated!

Yes. There are loads of threads about the ins and outs, but basically the only way you don't have to file is if you renounce your US citizenship. 

Ah ha, thanks.  I better get on with it then I looked on the American Citizens Services website and I think I only need to file for the last 3 years (rather than going all the way back).  Is my 'foreign earned income' my NET UK salary then if I've already been taxed by the UK?

No - Foreign Earned Income is gross earnings from employment (eg salary, bonus, company car, company provided life insurance and benefits) plus employer contributions to UK pension plans. The employer contributions are however treated slightly differently in that they do not always qualify to be excluded using the foreign eaned income exclusion.

In addition to filing tax returns with the IRS you may also need to file forms TDF90-22.1 with the US Treasury.  You will need to demonstrate reasonable cause why these are late if penalties are to be avoided.