We are a little late spotting this one, but better late than never!
If you book a Hertz car between 1 January and 28 February, for a rental up to 31 March, you can earn TRIPLE Avios in Iberia Plus!
Iberia Plus is already a good deal for crediting Hertz rentals, since you earn at least 300 Avios per day, and more for a larger car. This deal will get you 900 Avios per day (so 2,700 for the minimum 3-day rental required).
Despite being an Iberia promotion, it is valid for rentals starting in a number of European countries, including the UK.
Full details are here in slightly broken English.
Note that you need to use the relevant Iberia ‘CDP’ (rate code) for your Iberia status tier and enter the relevant ‘PC’ (promotional code) number. The rate you get this way may not be the cheapest out there, so compare before you book.
You will need an Iberia Plus account for this, but once the Avios have posted you can transfer them to BA or avios.com using ‘Combine My Avios’.