Opposition Senator Jeanne Atherden has been accused of having a tenant unknowingly pay both his and his neighbour's bills.

Stuart Anderson noticed the problem when his power bill plummeted after his neighbour moved out of a cottage also on Mrs. Atherden's property.

Lawyer Jennifer Haworth said her clients, Mrs. Atherden and her husband Maxim, had no idea Mr. Anderson was being double billed.

She argued the chartered accountant and his wife Kimberly, breached the lease by moving out early.

The Andersons are suing the Atherdens for $17,050 the total sum of their deposit and the value of the water and electricity they say they were wrongly charged.

The Atherdens meanwhile are countersuing for $18,981.70 in lost rent and damage to the Riddles Bay home.

Mr. Anderson told Magistrates' Court he moved to the property in May of 2008.

"In October of 2007, my wife gave birth to our third daughter, and so we decided that we needed a larger premises, closer to town," he explained.

"In August 2009, I became aware that I was paying for both Belco and water for a cottage on the lot without my knowledge."

Mr. Anderson added that the tenant of the cottage, taxi driver Cleveland Tucker, moved out in June and his own electricity bill plummeted.

"Our bills went down significantly," he said. "In August of 2009, I received a bill $450 less than the year before. That was the second month in a row it was significantly lower.

"I called Belco and asked if there were one or two meters on the property, and they said there was only one."

Mr. Anderson said he contacted Mr. Tucker, who told him that the utilities had been included in his rent.

"My belief is that they must have known about it," Mr. Anderson said. "Based on my experience with Mrs. Atherden, I can't believe she wouldn't know."

On September 1, 2009, Mr. Anderson sent a letter to the Atherdens, giving them notice that he intended to move out by October 31 that year.

"If I had known that before signing the lease, I wouldn't have entered into the lease," he said.

In it, he said he intended to leave the home in the same condition as when his family moved in. He also stated he would not seek reimbursement for the power and water bills if he received his security deposit back.

"At 10 a.m. on October 23 Mr. Atherden visited to inspect the home and receive the keys," Mr. Anderson said.

"We asked him if there was anything that would prevent us from getting our deposit back. He said there wasn't, and told us that he would talk to Jeanne and get back to us."

Mr. Anderson later received a letter informing him that because he moved out before the end of his two-year lease, he would not get his deposit back.

He claims that the Atherdens were themselves in breach. He said that contrary to the lease, the house was not freshly painted before he and his family moved in, and a hot tub on the property was never repaired.

Ms Haworth asked Mr. Anderson if he had used the power and water bills as an excuse to breach his lease.

"Rather than give them the opportunity to remedy the situation, you terminated the lease," she said. "Is fair to say at that point you weren't looking for compensation, you were looking for the lease to be over?"

Mr. Anderson replied that there had been several breaches of the lease already, and he decided he had enough.

Mrs. Haworth also put it to Mr. Anderson that the Atherdens didn't know he was being overcharged until he brought it to their attention.

He replied: "I understand that the property has been in their family for many, many years, and that various additions and renovations had been made to the cottage.

"I believe they knew, or should have known."

Under questioning, he admitted that he did not know for sure the financial relationship between the Atherdens and Mr. Tucker.

"I don't think the relationship either I or he had, was particularly normal," Mr. Anderson said.

The proceedings will continue on July 19.