Mystery Coolant Leak

[Guest]

I took Black Bess out to give her some exercise while I completed a couple of errands earlier today and she behaved normally throughout. However, while reversing into the garage after getting home I noticed a small amount of steam emanating from under the bonnet just ahead of the windscreen and there was also a slight odour of hot anti-freeze in the cabin. Left the engine running while I hopped out to pop the bonnet and take a look at the rear of the engine, as I suspected that coolant was perhaps being sprayed onto one of the heat shields, but found nothing. Clearly I am either looking in the wrong place, cannot see into the right space, or am simply losing a few more marbles. Theres no significant loss of coolant so if theres a leak somewhere its only slight but obviously needs attention.  

If anyone has had a similar experience and/or can point me at the probable source of the leak and how to verify it both myself and Black Bess would be very grateful.

Many thanks in anticipation.