That article you have quoted is from 2014. I've flown through London in both 2016 and 2017 and never had my cellphone checked in that manner.

As for your other question, you should have both a USB charge option and plug-in charge option in WTP. US plug should work fine - the plug will be set up to accommodate UK, US, and Europe plugs but in the worst case scenario you should be able to use your UK adapter (not a UK charger but rather plugging your US charge cable into the US to UK adapter) as a go between.