Already under strain from a boom in tourism and immigration, now New Zealand is braced for the arrival of 20,000 rugby fans next month

Keith and Jane Mackenzie are preparing for an invasion to engulf their Wellington home.

The Mackenzies are one of around 1,000 Kiwi families who have responded to a looming crisis about how New Zealand, already groaning under the strain of record numbers of tourists, can play host to the thousands of British and Irish Lions rugby fans preparing to travel round the globe to support their team in the forthcoming clash with the All Blacks.

They have offered to host Lions fans for free, many also offering pick-ups from the airport, guided pub tours and home-cooked meals.

The Mackenzies have three supporters, all strangers, coming to stay in the spare room – and they have little time for the hoteliers who have ramped up their prices to cash in on the rugby tour. “Those ratbagsstarted ramping the accommodation prices up for the Lions tour as soon as it was announced,” said Keith, 68. “So we thought, we can get around that. We’ve got room.”

“When we’ve been overseas, we’ve benefited hugely from the kindness of strangers,” said Jane. “So we are paying it back – or we are paying it forward. Whichever, it will just be fun.”

Less than three weeks before the start of the British and Irish Lions tour of New Zealand, the country is bracing itself for the influx. While excited about the sporting battles to come, and welcoming the flood of visitors from abroad, some residents have been voicing concerns about the lack of available accommodation.

For this rugby-mad nation of 4.7 million people, this Lions tour is the biggest sporting event since the World Cup in 2011, which the hosts – the All Blacks – went on to win. The last time the Lions – a combined team from England, Wales, Scotland and Ireland – toured “the Land of the Long White Cloud” was 12 years ago, but this once-sleepy island nation has since been transformed by a boom in tourism and immigration. Fans returning to the country where rugby is almost a religion will notice the change – fewer beds available, more campervans on the road and far less room at the bar.

In 2016 a record 3.5 million people visited New Zealand, an increase of more than 16% on the previous year. It is projected that by 2023 more than 5 million people will visit every year, spending NZ$15bn (£8m) a year. Tourism is largely welcomed – it is the country’s biggest earner and employs more people than the farming industry. But as visitor numbers have continued to rocket – largely bolstered by increasing numbers of affluent tourists from China and India – there have been growing concerns about the long-term effects on New Zealand’s once pristine natural environment.

Facebook Twitter Pinterest Jane and Keith Mackenzie, of Wellington, New Zealand, are hosting Lions fans in their home through the Adopt-a-Lion scheme. Photograph: Eleanor Ainge Roy/The Observer

Frequent reports of tourists washing and defecating in rivers and parks and on beaches threaten to taint the country’s reputation as a clean, green paradise, and basic infrastructure in the country’s most popular regions is under extreme pressure.

Last week the government announced a NZ$178m tourism package for the regions, to be spent on public toilets and car parks, and upgrading the “great walks” – a set of popular tracks for exploring some of the most scenic parts of the country’s backcountry – including introducing two new walking routes to ease pressure on the existing tracks.

However, critics claim the package is nowhere near enough to meet demand, and without an urgent increase in funding and better management, New Zealand’s renowned natural beauty is at risk of being spoilt.

The upcoming Lions tour will only add to the pressures caused by the record tourist numbers. Campervans, freedom camping – where camping is permitted on public conservation land – and Airbnb, the home letting website, have become the preferred means of finding accommodation.

More than 20,000 Lions fans are expected to travel to New Zealand for the six-week tour, which begins with provincial and club matches before the first Test in Auckland on 24 June.

With a general election only months away and a devastating earthquake just six months ago, visitors should be prepared for a country in flux. The government has invested more than NZ$3m to help the seven host cities – five in the North Island, and two in the South – prepare for the tour. Those attending every game will have to travel more than 3,000km.

Accommodation was identified early on as the biggest potential stumbling block for the huge numbers expected, with mainstream accommodation in the smaller cities already sold out.

In Wellington, 95% of hotel rooms are already booked, said Warrick Dent, general manager for major events for the Wellington Regional Economic Development Agency.

Since January, Airbnb accommodation in the capital has been advertised at up to NZ$2,000 a night, a “concern” for Dent and his team, but nearly impossible to control in a free market. The situation is such that, in an extraordinary move, the car park of New Zealand’s national museum, Te Papa, is being turned into a temporary camping ground.

Between 1,500 and 3,000 campervans are expected to descend on Wellington for the second Test match on 1 July, with 80 people booked to camp outside Te Papa. Campervans are also set to take over nearby Evans Bay and Shelly Bay, a former air force base.

Many visitors, outraged or unable to afford the steep Wellington prices, have chosen to stay as far afield as Palmerston North, a two-hour drive north of Wellington, or in the outlying rural communities in the Wairarapa, who are actively courting tourist dollars with special trains and free events.

Adopt-a-Lion: New Zealand rugby fans offer to host British and Irish free of charge Read more

The competition for reasonably priced accommodation has become so acute that an old-fashioned billeting system has been set up on social media – called Adopt-a-Lion – with Kiwis offering spare bedrooms, sofabeds and even gardens to fans who have been unable to find a place to stay, or can’t afford the high prices.

While visitors battle to find a bed, out on the Wellington waterfront, with its view of the South Island on a clear day, the foreshore is being prepared for a rugby party.

Ngati Toa, one of the local Maori tribes, is planning to dig pits metres deep around the lagoon for a traditional hangi feast for up to 500 visitors. Slabs of pork, lamb and beef, with sweet potato and cabbage, will be cooked in the traditional way: buried beneath the sandy soil, then dug up on the Saturday night, a couple of hours before kick-off.

The Churchill pub in Lambton Quay, a few streets back from the Wellington waterfront, has put in an order for thousands of litres of British beer to cope with the influx of rugby fans. The owners have also placed bulk orders for beef wellington, gammon, and bangers and mash.

“We have huge barrels of English real ale coming, thousands of litres,” said Tom Howarth, the Manchester-born manager of Churchill’s, which has installed a red telephone box to offer free access to the video chat service Skype for Britons to call home. “We also expect to dish up about 2,000kg of chips, and we’ll hire someone to sit next to the beer chiller permanently, with a radio for re-stocking.”

The pub has also hired extra security guards for the duration of the tour – all former rugby players.

“But whoever wins, the sun will still come up the next morning,” says Keith Mackenzie. “We just want to be a part of it all.”