I really would not recommend the Maycom AR108.
I used to own one a few years ago and sold it on ebay recently.
The audio quality and level is very poor and the sensitivity of the receiver is pretty rubbish.
I also bought a Yupiteru MVT-7100 from ebay and it is superb for airband using just the standard BNC telescopic antenna.
From what you say Robbie it sounds as though you live either in or v near to central London in which case you would need a quality receiver to pick up all the airfield ATC that you mention.
I live in Chelsea and can pick up ATC at Heathrow, Gatwick and City quite easily. I couldn't hear them on the AR108.
If you have an ebay account it really is worth searching on there for either a Yupiteru scanner or you can possibly pick up a really cheap (£5-£10) AR108 (if you really have to!).
DenhamPPL
PS: It wouldn't be worth making an external antenna for the Maycom. The sensitivity and selectivity is poor and any external antenna would most likely overload the receiver.