Any UK based pilot considering going on an equal time overseas roster needs to carefully consider their plans regarding tax. Tax free status and a 6/6 rotation are mutually incompatible under the UK regime (unlike many other countries
) Even somewhat appropriate rotations like 8/4 became more difficult when the days in the UK entering and leaving became accountable - where previously they didn't count.
The following document outlines the basics (replaces the former IR20 document that ceased to be valid last year):
http://www.hmrc.gov.uk/cnr/hmrc6.pdf
The following also has further links of interest:
HM Revenue & Customs: Residence and domicile: amendments to the residence and domicile tax rules