Centaurus,
AFAIK that metal banded strap was on RAF Navigators' watches while the pilots had a different strap. Its advantage was its ability to be fastened over a flying glove whereas Biggles had a clock on the IP.
At the first opportunity we would swap to a nylon strap, especially when we found one in sqn colours. The next generation were issued with a brown nylon strap combines with a leather backing. The nylon strap could survive ejection and the leather avoid nylon melt burns.