I can't see the UK going for just an MQ-4 solution - a P-8/Triton mix as with USN and RAAF perhaps, which would give mk 1 eyeball.
Regarding MH370 (Am I the only one who still thinks 'Spitfire' when they see that written?), the mk 1 eyeball isn't going to find an aluminium tube 4 miles underwater (Unlikely much else would either) and the surface searches haven't found anything anyway!