Brighton Pavilion Green MP Caroline Lucas urged television viewers to back voting reform in the referendum next week.
And she claimed that Brighton and Hove City Council could be about to go Green.
She was asked what would be a good result for the Greens in the local elections next week and flagged up places where the party hoped to make breakthroughs or gains.
She added: “In Brighton and Hove there’s a possibility that we could form an administration.”
On voting reform she urged viewers to vote Yes to AV (the alternative vote) to replace the first past the post system in the referendum on Thursday 5 May.
Challenged by Mr Neil that AV was far from perfect, she conceded: “It’s not our first best option but it is the best option on the table.
“It’s better than the present system.
“Many of us would like to go further but how do you get to that goal? Get a positive Yes vote next week.
“The No campaign has been very clever, to be polite about it.
“Frankly they’ve been telling lies.”
She accepted that a No vote would make further reform unlikely in the near future and added: “Don’t let the best be the enemy of the good.”
Ms Lucas said: “Under first past the post you can get an awful lot of power without an absolute majority.”
She said that with AV people could feel a lot more confident that they could vote for the party or candidate that they believed in.
She also defended her claim that the Greens are the opposition in the House of Commons even though she is the party’s only MP.
She said that the Lib Dems were in the coalition government so no longer opposed the Conservatives.
A lot of the present government’s policies were the logical conclusion of a lot of what Labour was doing, she added, citing tuition fee rises and market reforms in the NHS.
This left just the Greens to offer an alternative, Ms Lucas said.