I have had no 4G data connection around Greenford and especially in Ealing Broadway.
I would have to restart my phone in certain cases for it to work. The OnePlus 6 gives an exclamation mark on the 4G signal icon when this does happen. APN settings seem to be fine so some issue on your backbone network, also confirmed on the Mi 6X. On the bus to Uxbridge as well.
Switching to HSDPA does help in Uxbridge.
There is no usable data signal at all in Iron Bridge, this has been the case ever since joining Virgin last year, the rest of the areas are new issues 