OK, I have to admit defeat. There is, apparently, no village, town, or city in the UK that starts with an X!
There are plenty that start with EX, such as:
Exe – Somerset
Exe – Devon
Exeter – Devon
Exley – Calderdale
Exminster – Devon
Exmoor – Somerset
Exmouth – Devon
Exnaboe – Shetland Islands
Exning – Suffolk
Exted – Kent
Exton – Hampshire
Although the great google in the sky says that Exe exists in both Devon and Somerset I can only find the River Exe, which I was aware of.
It rises at Exe Head, near the village of Simonsbath, on Exmoor in Somerset, 5.2 miles from the Bristol Channel coast, but flows more or less directly due south, so that most of its length lies in Devon. It is 35 miles long.
The longest river in the UK is the River Severn which is 220 miles long and has the greatest flow in England and Wales. It has been the source of a great deal of flooding recently.
Not that any of this gives me a limerick, so here goes.
Sexy-Sadie from Exe in Devon
thought she’d died and ended in heaven
but sad to recall
she had suffered a fall
and was drowning quite fast in the Severn