I am on a 40/10 Contract with EE.
Generally the BTW Tests have been consistent with that, about 37/8.
However over the past week, frequently first BTW Test each morning around 07:00 has been astonishingly high, over 100/8, an extreme being 148/8.
On a couple of days, similar has happened on the first of a group of BTW Tests, repeated to be a group due to the high first reading.
With those very high readings, there has been no obvious shortening of the initial "setting-up", before the 5 second count-down and actual tests - With the 148/8 test, that setting-up period was in fact unusually slow initially, followed by a pause, then bormal, in to the 5 second count-down.
TBB readings have been "normal" at about 36/8, taken immediately after.