Senator Sam Mezec says the Environment Minister's political legacy will be one of failure if he doesn't show stronger leadership and commit to supporting policies to increase the supply of affordable homes in Jersey.

Deputy John Young told the States Assembly that he supported Senator Mezec's plans to boost affordable housing provision at the Waterfront and South Hill 'in principle'.

However, Senator Mezec called that a 'cop-out used by Ministers to sound good, but not actually vote for the change that would tangibly improve the situation.'

That proposition, which is to increase the provision of affordable housing at the Waterfront from at least 15% to no less than either 30% or 50%, will be debated by States members later this month.

In guidance published this summer, the government said at least 15% of homes built on this site should be affordable for first-time buyers to acquire.

That equates to 23 out of 150 properties on South Hill and 150 out of 1,000 properties on the Waterfront.

Senator Mezec asked Deputy John Young whether he'll commit to backing his proposition, which will help to protect green space elsewhere.

"I 100% want to achieve as many affordable homes as we can.

"The Senator, I think he's not clear as to whether he wants me to commit now to how I'm going to vote in three weeks' time.

"I think, hopefully, that (States) members will understand that that would be wrong, it would be pre-judging. I've got to listen to the advice."

Deputy Young is facing pressure over the plan to build homes on some green space in the coming years to meet the huge demand.

Several politicians have lodged challenges to the island plan to stop that from happening in their parishes.

Independent inspectors will look at the plan later this month.

The plan is to build 4,150 new homes by 2025, of which 1,500 would be affordable for rent and purchase.

Deputy Montfort Tadier questioned whether Deputy Young risks being known as the Minister who 'concreted over the countryside'.

Deputy Young says if that's where we end up, he'll probably be out the door.

"No, I'm not prepared to stand in this assembly and put a final Island Plan through for approval that does what the Deputy said."

Senator Mezec has lodged two amendments to the Island Plan - which are:

• To require private developers to make an affordable housing contribution
• To make sure planning permission wouldn't be granted on government-owned or government-owned bodies sites unless they meet the planning guidance definition of 'affordable'.

The Reform Jersey leader called the Environment Minister's 'in principle' support of these ideas 'not good enough.'

He then asked whether he'd commit 'to being on the right side of history' and vote in support of a proposition to increase the supply of affordable housing.

"Legacy, eh? The right side of history, wouldn't that be nice?

"Look, I'm going to make my judgement after I hear what the inspectors say and I've told the assembly that there is a line in the sand that I won't go beyond.

"An adequate level of affordable houses on States-owned sites and personally I want to see a contribution from privately-owned sites as well, I want to see that and that is why the comments I've published to the inspector are supportive, in principle, but I can't pre-judge here today.

"We are now five months away from that decision, (on the Island Plan) there is a lot of water to go under the bridge in this, and to stand here now and pre-judge is not what I'm prepared to do."

Senator Mezec also quizzed Housing and Communities Minister Deputy Russell Labey on whether he thought 173 affordable homes out of 1,250 on the Waterfront and South Hill sites 'is a satisfactory contribution, when there are 3,000 applications on the Affordable Housing Gateway'.

Deputy Labey says 1,426 are waiting to buy on the gateway, 641 who want to move from private rental, and 423 current Andium residents who want to move to another Andium property.

"I will not be satisfied until we have caught up with the 2,000 fewer homes than we should have built in the decade from 2010 to 2020, until we have smashed that waiting list on the gateway, until we've provided all the affordable projects that we can to satisfy the market, but I have to say I am concerned about elements of the Senator's proposition.

"If we combine with banning States of Jersey Development Company to develop Category B housing units on States-owned land, ban that at the same time as introducing mandatory H3 for the private sector, that worries me because whilst the affordable housing is a total priority of mine, we absolutely must supply the open market, otherwise it's going to continue to inflate and that has ongoing issues with our ridiculous housing prices."