The NATS AWARE mentioned above is a very good, inexpensive colour chart position showing GPS device. It has the free monthly CAA chart updates too.
[I understand 1/4 mill & French charts etc. are now available too].
Its Controlled Airspace warning and mapping is a perfect way to prevent "busts"
I've had mine a year and it's so easy to use. They sell bigger & better models too, but IMHO the original £150 model is perfect.
mikehallam