Almost correct there 5 miles, LATCC(Mil) work it across the FIR boundary (NAVPI) to Marham. The aircrew always file NAVPI CSL MAM BZN DIKAS GAT, in reality they get NAVPI MAM DIKAS GAT.
The handover to Swanwick Mil is usually around Marham with Swanwick obtaining the CFP through the Alphas usually at the level requested by the pilot (FL280+ mainly) and the subsequent join at DIKAS, as there is little point in giving the aircraft back to LATCC(Mil) West for the bit over Oxfordshire etc.
Afterall, from May Swanwick Mil will be West!!!
The Westcott is sometimes on this route used for the heavies out of MLD for DIKAS