Thousands of horses are being abandoned or tied up and left to starve, many by desperate owners unable to afford the costs of keeping them. A national crisis has seen Britain's biggest horse charities under unprecedented pressure from the sheer number of animals needing their help.

Redwings – Britain's biggest charity for abandoned horses – says the situation has reached breaking point. It has seen the number of cases soar from 160 horses in 2009 to 450 last year. So far this month it has taken in up to 10 a day. The charity, which can house 1,200 animals, is now full.

Hundreds of other horses around the country are not so fortunate. Left to fend for themselves, they are savaged by dogs or fall victim to drivers on Britain's roads. The national situation is hard to quantify, but the RSPCA is aware that at least 3,500 horses are left chained or tied up without shelter at any one time. The charity estimates it received more than 7,000 calls in 2011 reporting horses and ponies that had been left tied up – up 21 per cent on the previous year.

Britain is seen as a nation of animal lovers and thousands are expected to flock to cinemas to see Steven Spielberg's War Horse. But, as the recession bites, owners are increasingly desperate, an IoS investigation timed to coincide with the film's release shows. The Blue Cross animal charity estimates the average cost of keeping a horse has almost doubled in the past five years, from £3,600 per year to £6,000.

Nicola Markwell, Redwings' communications manager, said yesterday: "Our latest rescues have involved 19 horses dumped on Bodmin Moor and another left in a colliery in Wakefield. We can't take any more. But some people have taken down our fences and put their horses inside, hoping we won't notice."

Many animals do not get that far: increasingly, new-born foals are being killed, particularly mares which are unlikely to raise any money. Many more horses are being sold for meat. Zoos are among those that benefit: a single tiger can get through 15kg of meat a day. Government figures reveal that almost 8,000 horses were slaughtered for meat in 2010 – a 50 per cent increase on previous years.

A combination of rising costs of essentials like hay and straw, along with a drop in the value of the animals, has created a vicious circle in which horses suffer, according to campaigners. Even charities such as the Blue Cross, which get discounts for bulk buying, have seen a massive jump in costs in the past year – the price of a bale of hay has risen from £2.50 to £4 in some areas.

The falling value of horses means they can change hands for as little as £5. Many are killed before they reach six months, by which age owners are required by law to register them.

Andrew Elliott, an auctioneer at Brightwells in Leominster, Herefordshire, one of the largest horse dealers in Europe, said: "For the very best horses, the cream of the crop, prices have pretty much held up, but in the middle and lower ranks prices have collapsed.

"There was a huge demand for horses, and some of the breeding was pretty indiscriminate, trading was becoming relentless and then, in the autumn of 2008, the bubble burst. I don't like to use the word 'cleanse', but the horse industry is a huge business – it was over-producing and it has to be adjusted."

Increasingly, owners are leaving horses tied up and uncared for or abandoning them altogether, a practice condemned as "extremely dangerous" by Sally Learoyd, the RSPCA's equine rehoming officer.

"We have seen ponies strangled to death by their own tethers and with permanent neck, leg and hoof injuries, all as a result of the animals being tethered," she said.

In Bradford last year, inspectors found a Shetland pony, Susie, with a chain embedded so deeply in her neck that tissue had begun growing through the links. Fortunately, they managed to save her and the pony has since been rehomed.

The upsurge in problems with horses is part of a bigger picture of abuse: the RSPCA gets hundreds of calls each year about horses, ponies and donkeys that have been cast aside.

"Most of the horses brought in by inspectors have been starved and neglected, and many aren't used to human contact because they have never been handled properly or been treated with kindness," Ms Learoyd said.

As well as cruel neglect, some horses face deliberate sadism.A stallion in Stithians, near Falmouth in Cornwall, was mutilated and killed last week. The attacker cut off the animal's genitals, cut out one of its eyes and pulled out its teeth. Just days earlier, a pony had been similarly attacked and killed in a field in Whitland, near Tenby in west Wales.

Many animals are simply turned loose by owners unable, or unwilling, to pay the hundreds of pounds it costs to have them destroyed by a vet.

But the plight of horses in Britain today is part of a wider picture of animal neglect. The credit crunch has proved a tipping point as many households struggle to cover the costs of keeping pets.

Record numbers of people are reporting animals that have been discarded – there were more than 28,000 calls about dumped pets in 2011, according to new figures released by the RSPCA last week. This is the highest number in five years and up a third on the 21,481 in 2007.

Cases of stray and abandoned animals dealt with by the Blue Cross have risen 28 per cent in the past year – from 1,553 in 2010 to 1,991 in 2011.

And the number of people giving up pets because they cannot afford to keep them has doubled, according to Battersea Dogs and Cats Home.

Vicki Alford, equine manager of the Blue Cross animal rehoming centre in Burford, Oxfordshire, said: "We have seen some shocking cases of neglect in recent years, as well as people making the heartbreaking decision to give up their horse because they just cannot cope any more."

Market forces: 'Animals change hands for a fiver'

The fact is that we have got far more horses and ponies in this country nowadays than we can legitimately deal with. There are more horses than there are homes to care for them and there are literally hundreds of horses out there suffering.

The problem is that people have thought for far too long that breeding horses is an easy way to make money. But the reality is it isn't that easy. There's a small market for the top-end horses and too many people have ill-advisedly produced what are essentially poor-quality animals.

I could easily take you to a horse sale at the lower end of the market where they are changing hands for a fiver. They get treated like something that's worth £5, to be honest They get bought by people who think they'll be able to make a few quid on them, which they won't and, because they are essentially worthless, they get treated like they are worthless – and that's the sad reality.

Abandonment has been a massive problem over the past few years, probably due to the general economic climate, but the level has gone up hugely in the last couple of years. We would estimate it's gone up by about 50 per cent in the last couple of years, which is quite significant... it's in the high hundreds annually.

The thing that the film War Horse brought home is the bravery and the suffering horses went through in the First World War. It's easy to think that today we've moved on and that we treat animals more favourably; the reality is that the role of horses has changed massively over the last century or so. They've gone from being very much work animals to leisure animals.

Unfortunately, that hasn't necessarily meant their lot has improved on the whole, and the big problem that we face today is the over-production of horses.