The laws of TUPE are amazingly vague, and (I believe dealt with on a case-by-case basis).
A few ex-colleagues of mine, went (via TUPE) from Servisair to GATE aviation when the EZY contract changed hands at NCL. The stories I have heard are quite frankly amazing.
Servisair staff, are on a higher rate of pay, with better holiday entitlement and callout fees etc, and sick pay... that their counterparts who were part of the original Gate Aviation payroll.
Just before the TUPE came into effect, Servisair promised its staff a pay rise. But between agreeing the pay rise, and it coming into effect, the TUPE happened. GATE are now obligied to pay the ex-servisair staff the pay rise that they would have got without TUPE. Naturally the original Gate Staff are entitled to nothing, and fall further behind.
On the flip side, any pay increase to Gate employees, has to apply to TUPE staff too. I am also told there is NO TIME LIMIT on their TUPE agreement either. Its all down to what was agreed at the time.
RTG!