Yes, Homebriefing is an excellent service. One of the well kept secrets in this business.
A little less suitable for flight plans for UK-style IFR (OCAS) because they stuff all IFR flight plans into CFMU and low-level routes in the UK around Class G etc usually violate airway MEAs etc etc so UK ATC nods and winks and addresses them manually as if they were VFR.
But then few people file flight plans for that sort of flying anyway (no legal need to).
When you say
MOCA I think you mean
airway MEA 
This is normal - you have to remain OCAS after departure, until London Control take you over. MOCA is obstacle clearance; an FAA-only term!