Sentinel perhaps?
Not sure exactly what its role is but it is certainly designed for an overland role which is what we are using the Nimrod for at the moment.
E3 perhaps?
Then if we decide we need an immediate and interim ASW platform, lease P3.
Given that we only 'need' 12 MRA4, which would allow for through life attrition, this suggests that in the interim we would need only 5-6 platforms.
Even a C130 modification programme a la AAR post-FI, might suffice.
Apart from the pure ASW role I suggest we have enough suitable airframes.