My biggest concern about this idea is that if it happened at some point in the future there would be a decision whether to invest £xbillion in upgrading/maintaining it or spend that money on the NHS or something similar. The obvious outcome is that if the goal of delivering fibre by British Broadband is ever achieved (which I very much doubt, let alone to timescale and budget) it will slowly fall apart over time due to lack of investment and will slowly become over staffed/over bureaucratic and expensive to maintain and run.
At some point we will therefore end up with a two tier system for those that can/want to afford it whilst the BB slowly rots.
I wonder what will happen to all the extra staff required to get this done in the timecales too as presumably they would never be laid off.
I also wonder what is to prevent all the internet companies who face picking up the bill for this simply pulling out of the UK. I look forward to reading exactly how this tax will be imposed.