How many authorities are there to count in the UK? BBC says 205 have been counted. Are they the same as parliamentary constituencies?
No, they use local authorities. 326 in England, 32 in Scotland, 22 in Wales, 11 or 26 in NI (depends if they use previous or next authorities). At least one will be missing tonight, as there is some backwards religious islands in Scotland refusing to count on Sunday, since it's a day for God, if I remember well.
Northern Ireland has a single count under the jurisdiction of the Chief Electoral Officer, who is responsible for everything election-related in the province.