I think I tightened the roundish silver locking plate inside handlebar stem a little, which has two Alan screws & slides back and forth and locks into the headset, meaning I now can't fold the handlebar stem.
Was simply trying to tinker with the tightness of the handlebar stem QR not realising that that is only controlled by the nut with white plastic spacer.
Have tried budging the silver plate backwards from the outside by using a thin dinner knife through the slit on the headset but it won't budge. Removing the handle bar stem QR lever isn't possible - even if that were to help. Can post pics if required.