It is possible. I am carrying out due diligence on a wide-body commuting job in Asia that is akin to part-time with blocks of days off each month.

As there would be at least 6 trips per year in a working capacity as a crewmember in or out of LHR, the third UK and overseas statutory residence tests (SRT) would not apply, as HMRC would view it as a ‘Relevant Job’ and I would therefore be exempt from those SRT tests. Providing I do not spend more than 183 days in the UK and since I own a second residential property in Spain, which I would spend more than 30 days at every year, then my maximum number of days allowed in the UK would be determined by my number of ties I have to the UK as set by HMRC.

It would allow me 120 days in the UK with every third year allowing me up to and including 182 days. Spain is far easier to assess as the threshold is 183 days and as I have no family living there permanently, plus given I would spend more days in the UK than in Spain, they could not class it as my primary residence either. I would therefore not meet the residence criteria for income tax purposes.

Sorry for the long winded explanation and for the thread drift from the OP's initial topic.

Correct me if I'm wrong, but I think the tax break in Portugal is only for retirees.

Depends which "tax break" you are thinking of. According to one or two conversations I have had with Portuguese residents there are certainly some financial advantages to be had by living there even if you are still gainfully employed.