The cyclist admitted to taking the blood-boosting agent EPO eight years ago.
Millar was banned under a BOA bylaw but the Court of Arbitration for Sport will announce today that such a punishment is to be overturned. The lifetime bans imposed on sprinter Dwain Chambers and shot-putter Carl Myerscough are also to be lifted.
The BOA, who last night refused to comment on the CAS ruling, will have no choice but to accept the decision. They will instead turn their attention to changing the WADA's global code on doping.
They have proposed a minimum four-year ban for a first serious doping offence, including missing one Olympics, with national Olympic committees having the autonomy to deliver tougher sanctions if they so choose. However, any such agreement would not come before the London Games, so Millar's and Chambers' participation will not be affected.
Most anti-doping experts believe that it is more likely that the WADA will agree to change their code to increase the length of a ban for a serious offence, but will stop short of allowing individual Olympic committees to have different sanctions.