This petition was rejected

The Government e-Petitions Team gave the following reason:

The decision was taken by Clearcast, who are a private organisation. They preclear adverts on behalf of broadcasters before they appear on television.

You can find their statement here:

www.clearcast.co.uk/blog/clearcasts-md-responds-to-coverage-of-their-decision-not-to-clear-the-iceland-ad/

Broadcast adverts are covered by the UK Code of Broadcast Advertising. The rules on political advertising are the responsibility of Ofcom, and not the UK Government or Parliament.

www.asa.org.uk/codes-and-rulings/advertising-codes/broadcast-code.html

You could start a new petition calling for changes to the way advertising is regulated in the UK if that is something you would like to see happen.