The FIA has announced it will allow in-season engine development until at least the end of the 2019 season.

A token system was introduced at the start of F1's hybrid formula in 2014, with 'spending' allowed throughout the season just gone after Ferrari discovered a loophole in the regulations.

As before, the number of tokens an engine manufacturer might spend on development tapers off through to 2020, although more will be allowed year-on-year.

Therefore, 32 will be permitted in 2016 instead of the 25 previously allowed, with 25 in 2017, 20 in 2018 decreasing to 15 in 2019. Previously, manufacturers could spend only two tokens that year.

In addition, token levels have been set for new engine manufacturers entering the sport after Honda were given an average of the number Mercedes, Renault and Ferrari had remaining by Australia this year. That figure was worked out at nine.

In the future, a new manufacturer will be allocated 15 tokens in their first year, and 32 in their second.

Power unit tokens allowed for in-season development

2016 - 32

2017 - 25

2018 - 20

2019 - 15

New manufacturers

First year - 15

Second year - 32

The rules have also been tweaked to allow power units homologated in previous seasons to be re-homologated. Previously, no manufacturer could supply more than one specification of power unit.

This allowed the FIA to approve Ferrari supplying a fourth customer team, thought to be Toro Rosso, with a 2015 engine next year.