V1GO:
A couple of points -
The Transair shop in Victoria (50a Cambridge Street) is rather small and doesn't carry as much stock as those at Shoreham and Fairoaks. Fairoaks refunds your landing fee if you spend more than £50 at Transair.
I've found Biggin Hill to be an excellent airfield with the most helpful staff, whatever I was flying. However, it has the drawback of having poor transport links with central London - something it shares with Fairoaks.
Red Four is right; Rochford station is very close to Southend and has frequent services to Fenchurch Street station in London. It's also worth thinking about Redhill, from where you can either take a five minute taxi ride to Redhill Station and a train to Victoria, or a 15-minute taxi ride to Gatwick and catch the Gatwick Express into town.
Whatever you choose, I'm sure you'll find that London area ATC is courteous, helpful and professional. Enjoy.