Shortly afterwards I received a letter from the planning office saying
that I needed to apply for planning permission (with plans + full fee
of £220!).

Odd. When I was considering converting my garage, the council said that it
did need planning permission to remove a restriction on conversion made when
the estate was built. However, they said that as it would otherwise not
require permission, that the fee would be entirely waived.

Apparently, their plan calls for two off street parking spaces for every
house of this size. The defined a parking space as being 2.4m x 4.8m. The
drive was only 9m long, hence 60cm too short. We would probably have got
permission, but moved house before the conversion.

We were planning to get an ultra large scale plan from the OS and photocopy
it at a few % enlargement and write "Not to scale" on it. We were advised to
do this by a builder friend, who said it often worked and wasn't illegal.
The planning bods would normally ignore the "not to scale" marking and read
distances off with a ruler.

Even so, I suspect permission would have been granted even if they knew the
length.

Christian.