Start here;
Types of tax : Directgov - Money, tax and benefits
I do not wish to alarm any of you who are not paying any tax right now, but;
Within the EU, regardless of where you live, regardless of where you work and regardless of where you are paid, you are required to pay both tax and National Insurance.
The rules governing payment and liability of tax and NI within the EU are many and varied, however, unless you are not working or have no income from any other source, you will be required to pay tax, even if you are retired.
The tax will generally be deducted from the country where you derive the majority of your income, so if you work for BA then you must pay tax in the UK.
Be very careful when you make any attempt at full or even part time employment within the EU and refrain from paying any tax. The penalties can be very severe. Remember what happened to Boris Becker and Michael Schumacher, who didn't declare income made outside their country of residence, thinking they were exempt somehow. They were not and only avoided prison by paying ALL of the tax they owed plus a hefty penalty.
No-one is exempt from paying tax. If you do evade paying you are committing a crime. You can and almost certainly will be found out eventually.
My advice is to speak to your tax officer, make a declaration to him, in full and pay any tax you owe promptly. Working in country A and living/commuting in country B or C and being a citizen of country D or E makes no difference. Within the EU makes you liable.
Death and taxes, much the same reaction to them both and both unavoidable.