Polio is not on the rise in UK.
There have been no cases.
What has been found is samples containing vaccine-strain polio virus in sewers in London. This would have come from someone recently vaccinated arriving in UK from one of the countries that still uses the oral live vaccine (which sheds via faeces)
It shows how good our monitoring systems are that these sorts of things are still looked for, and that when found, action is taken.
Remember the oral live vaccine was in use here until 2004 (one of my DC was among the very last to have it that way) and the sewers must have been absolutely swimming in it, as it's likely many parents who touched nappies of newly immunised infants would have had a reinforcing dose and passed it on.
Vaccine strain is unlikely to cause severe illness (if it causes illness at all) but the risk is there - it's why you used to be told not to take DC swimming within however many weeks it was of oral immunisation. Risk is mainly to the never immunised, or to those for whom the vaccine did not 'take' properly
But even when, prior to 2004, there was lots in our sewers, actual cases of vaccine-acquired polio were very low (may even have been zero)