Found this thread about a similar problem with the Enviro+ Envio+ BME280 temperature and humidity fault.
It looks like there may be a problem with using the BME280 outdoors, although my Enviro Urban was in the recommended enclosure.
I have got round the built-in BME280 not working by adding an external BME280 breakout, the only problem I discovered was that the built-in BME280 of the Enviro Urban is on address 0x77, not on 0x76