I read somewhere that if you have a YP railcard linked to your oyster
card and you make a peak journey in the evening, you will be charge
the offpeak rate. The reason being is that if you purchase an off peak
travel card you can use it in the evening during peak time time. I
was surprised to learn that I made a journey from Kings cross (LU) to
Hounslow at 5pm and it charged me £4.30. It should have been £1.70?

Can someone please clarify.