As reported by Points to be made, You earn double BA Avios until end of the year. You must register before August 31st, 2020 for travel by December 31st, 2020.

I received the offer from BA this morning via email, see details below:

• You can now enjoy double Avios on up to 10 flights or holidays. All you need to do is register and book by 31 August 2020 and travel by 31 December 2020.
• A Qualifying Flight is a single leg of a journey that departs from one location and lands in another, e.g. Edinburgh to London.
  

  They can be booked as a one way, return, multi trip booking or as part of a holiday, where each individual leg counts towards the maximum of ten flights.

  One-way example: New York–London with no return would be one Qualifying Flight.

  Return example: New York-London-New York would be two Qualifying Flights.

  Multi Trip example: New York-London-Edinburgh-London-New York would be four Qualifying Flights

• This includes all domestic flights in the UK, and within southern Africa. 
  
• Also included are our British Airways flights operated by our partners, American Airlines, Iberia and Finnair, when travelling between Europe and North America.
  
• *Double Avios on flights can be awarded to all global Executive Club Members. Double Avios on holidays can only be awarded to Executive Club Members who are registered in the UK or USA.