If you head out to the shops today, or a churchyard, or a school, or a playground, and you live in a town or city, you might be in for a surprise. Cats, dogs, squirrels, even foxes are part and parcel of our urban landscapes now but increasingly, it’s not out of the question that you might just as easily meet a deer.

The deer population in the UK is at the highest it has been for at least 1,000 years, at around two million. Over the past few decades, does and stags have been spotted in urban areas and villages around the UK, from Glasgow, to Sheffield and London. This week, the Royal Horticultural Society released guidance on how gardeners can deer-proof their outdoor spaces. Replace tulips with daffodils and red hot pokers, it suggests, because deer don’t like the taste and it will stop them rummaging through your flowerbeds.

So how did deer come to wander into our back gardens? For a start, population growth. Accurate data on exact deer numbers is scarce because the animals are secretive with a significant range. However, there is evidence that numbers of red, roe and muntjac deer are increasing. In Scotland, the deer population has doubled in the past 50 years. There are many reasons for this: since wolves, lynx and bears became extinct hundreds of years ago, deer have had no predators to contend with. They, along with other wildlife, have also benefited from other factors including milder winters, increased woodland cover in some areas and changes in farming such as the planting of winter crops.

A fallow buck in an urban environment. Photograph: Jamie Hall/Alamy Stock Photo/Alamy Stock Photo

Urbanisation is another factor. As towns and cities expand into the countryside, the wildlife populations that were already there still need to eat. The increasing sightings of urban deer being reported “gives the impression of deer coming into urban areas, but it’s really urban areas going to where the deer are,” says Sam Hamer of Dorset Wildlife Trust. “Where once there was woodland or a big field, there’s now a housing estate.”

And deer might be getting a helping hand from their new neighbours. “Numbers are increasing partly because they are encouraged by people feeding them,” says Fiona Mathews, professor of environmental biology at the University of Sussex.

Deer are opportunistic herbivores – they are not fussy about what they eat (unless it’s tulips). “The urban area offers huge possibilities in terms of food,” says Ian Rotherham, professor of environmental geography at Sheffield Hallam University, who has studied populations of deer in the UK since the 1980s. “If you’re a muntjac getting into an allotment, who knows what’s on offer for you? It’s easy pickings.”

Since the 1970s, deer have been making their homes in urban woodlands and near rivers, which provide habitats, cover and safe corridors to allow them to find food and breeding opportunities. But the destruction of this land to make way for housing is pushing them from the suburbs into our town centres. In London, for example, deer have been spotted on railway cuttings in inner-London boroughs such as Islington and Lewisham and on housing estates in north-east London. “Deer would normally go between small patches of woodland,” says Stuart Edmunds, of Shropshire Wildlife Trust. But now “they haven’t got the covered habitat connectivity.”So, they are wandering in areas where they previously would have been hidden.

Not everyone sees this as something to worry about. “I think it’s superb,” says Mathew Frith, the director of conservation at London Wildlife Trust, who is working on a London deer strategy. “Large herbivores are beginning to navigate and tolerate the urban environment and find a home here, no matter how suboptimal it may be.”

What could be more magical than seeing an animal with antlers ‘like masts in a harbour’ near your local Tesco?

And for many people, seeing Britain’s largest wild land mammal face to face will be a moment of wonder. What could be more magical than seeing an animal with antlers “like masts in a harbour, or city spires” as the poet Kathleen Jamie put it, near your nearest Tesco Metro? Certainly, the presence of deer in built-up areas offers educational opportunities and the chance for people to connect with the living world. But reaction is mixed.

“If you see a deer from your garden, people are usually really excited. Whoa! It’s a deer! That’s great. But if a deer comes into the garden and eats your prize rose bushes or drops deer ticks in the garden, people get very unhappy,” says Rotherham, who has run surveys on public perceptions of the animals.

Their arrival also brings other challenges, such as road-traffic collisions. In Dorset, for example, deer will attempt to cross the M5 and the A35, which transect enormous stretches of the woodland they call home. Fallow deer, Britain’s most common species and recognisable by its fawn fur that spots white in summer, are crepuscular, and range large areas at dawn and dusk – about the times when traffic on the roads is at its peak. Fallow and sika deer (which are slightly darker) cross roads in single file, and they can drift in herds of 50 or 60, which increases the possibility of a fast oncoming car hitting them.

It is hard to say how the rise in urban deer populations is affecting wider ecologies. Deer don’t eat the same food as foxes and badgers, or compete for territories, so an impact on urban mammals is unlikely. There is a potential impact on insect populations if deer are grazing fruit-bearing plants.

A muntjac deer, which causes damage to woodlands. Photograph: FLPA/Rex/Shutterstock

Muntjac deer – smaller, stockier and russet brown in summer – are a concern, however. They eat everything, and a lot of it – including parkland, woodland and rare plants – and their numbers have increased rapidly. In Shropshire, the population has increased by 75% in five years. “A muntjac is quite a cute little thing, and exciting to see,” says Rotherham. “But they do do enormous damage to woodlands.”

So what is the future for deer in our cities? Might we one day see red deer stags rutting and roaring on Tower Bridge? Or will deer-management policies that happen in rural areas start to be implemented in cities? Could we even see calls for more “extreme rewilding”, reintroducing apex predators such as wolves and lynx, which historically kept deer populations balanced? How should we consider this rise in deer sightings and the relationship with our new neighbours?

“A lot of our urban environments have still got wildlife areas, which is a positive thing”, says Edmunds. “But like everything else, it’s about keeping the balance before it starts to have that detrimental impact.”