I've checked the postcode you have given on a couple of independent sights and they are all returning weak 4G and 3G.
The signal for your Son's phone will likely be supplied by EE. The 4G mast appears to indicate it is 800MHz 4G a frequency denied to Virgin.
I would have thought the town centre would be better served though.
There is little to be done for poor network coverage.
Virgin are in the process of moving over to using Vodafone, but there is no timescale as to the date that will happen, except this year.
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