Several days previously, news had broken of Australian supermarket chains Coles and Woolworths dropping some New Zealand products in a drive to become the "most Australian" supermarkets.
It "stuck in his craw".
"If it's good enough for the Aussies, it's good enough for us. Two can play at that game," he says.
Woolworths is the parent company of Progressive Enterprises, which owns New Zealand's 168 Countdowns.
So Lancaster set up a Facebook page "Boycott Countdown", and cheekily posted a link to it on Countdown's own Facebook page.
"I was sitting there and thinking, people are pissed off. I learnt from the Rena, it takes one person to kick the ball. Keeping it going is harder but starting it is easy and everyone can do it and you can have an effect," he says.
"I thought it would be news for a month or so and fade away. I thought it would be awesome if I got to 1000 likes."
A week later he reached the magic number.
And then something unexpected happened that catapulted it to a whole new level.
Under the protection of parliamentary privilege, Labour's economic development spokesman, Shane Jones, made allegations of unfair treatment of New Zealand suppliers on this side of the ditch.
He claimed Progressive Enterprises was blackmailing New Zealand suppliers into paying to keep their products on its shelves.
It is an allegation that Progressive Enterprise's managing director, Dave Chambers, "categorically" rejects.
Support for Lancaster's Facebook page trebled overnight. As this article goes to print, the number of "likes" has exceeded 7500.
"It's burning through my internet allowance ... it's keeping me amused," says Lancaster, who tracks its progress during the day via his smartphone.
"It wouldn't have been such a big thing if Shane Jones hadn't got involved."
Wearing a "I Walked the Milford Track" T-shirt, a memento from working as a guide on the track in the early 2000s, over a frayed thermal top, Lancaster is deceptively astute.
He has a degree in economics from Waikato University, a keen interest in current affairs and a compulsion for fairness.
Ultimately, he would like to see Countdown's profit reduced to zero. "If that happened I would like to see it sold. It doesn't have to be a Kiwi company, as long as it's not a company that actively discriminates against New Zealand products and people," he says.
He also argues that 10 per cent of Countdown's profits go to Australia - profits he would like to see stay here.
"Go to your local butcher, green grocer and supermarkets," he urges.
Fears of job losses are unfounded, he adds.
"There would be job transfers if Countdown started losing money. People in New Zealand still need to eat. Other retailers would be better off and hire more staff. It's not like spending is going to stop. There would be a change of mix where the retail dollar goes. There might even be some efficiency gains. A lot of economic wealth could be gained."
Tauranga chef Peter Blakeway is well-known for championing local food.
"I can understand from the point of view of the New Zealand exporter trying so hard to get good New Zealand product to foreign markets - how frustrating it is - but at the end of the day, if we took a step back and chose to eat local and in season: one, we would be looking after ourselves better and, two, we would be looking after the local economy better," he says.
"I'm biased. I firmly believe we should look after our nearest and dearest first. To my mind that means markets and local producers. If you widen it out a little bit, yes, other supermarket chains in New Zealand are owned by a large group of individual New Zealanders."
Blakeway says he tries not to use supermarkets, instead buying fresh produce from farmers' markets and direct from local producers but, when necessary, he shops at Pak'n Save.
"I'm very fond of Dean Waddell. I used to go to Brookfield New World, now I tend to go to Pak'n Save because it's his business. It's up to each of us ... if you're going to buy in a store you want to know who owns it, you want to know where the money goes and if it stays in the Bay," he says.
"As a consumer the only thing we can vote with is where we put our money and if we start to care where we spend our money we must start to really care where we spend our money."
Eating local and fresh also had its health benefits. "I firmly believe our food is so important. What we eat is the only thing that affects us in the short, medium and long term. It can protect us or hurt us."
Progressive Enterprises says the decision made by Woolworths supermarkets in Australia to support local farmers applies to a small number of own brand product lines and are not specific to New Zealand.
"There is not a ban on New Zealand products on Woolworths supermarkets shelves: there are many New Zealand producers who work successfully in the Australian retail market and have done so for many years.
"There are also examples on both sides of the Tasman where local customer preferences come into play - we choose not to stock Australian apples, for example," says Chambers.
With regard to the allegations of blackmail, Chambers says if any MP or supplier has questions or concerns they are welcome to contact Progressive Enterprises directly to discuss them.
"We will fully co-operate with any enquiries from the Commerce Commission," he says.
The commission has yet to decide whether to start a formal investigation.