Engineering works on Sunday meant that Thameslink line from Bedford terminated at St Pancras (higher level platforms) and those wanting to continue their journey southbound had to tap out at the higher level and then tap in again to access the lower level platforms. Very badly organised as the barriers upstairs were kept open with staff telling people who wanted to tap to go to the readers on the far right and those that didn't to walk through. So those trying to access the readers were crossing the onward sweep of passengers rushing for the north bound trains. Compounded by people trying to tap on the readers by the open gates which were switched off, then "reversing" to reach the readers. I digress, the fare for Elstree & Borehamwood to Blackfriars off peak should be £4.10, instead I was charged £4.10 E & B to St Pancras plus £2.10 St Pancras to Blackfriars. I've complained and no doubt I will be refunded eventually, but this overcharge will have occurred for many people who won't know to check and complain.