Behind the walls of Bangladesh's garment factories

In the hot and frantic city of Dhaka it seems garment factories are crammed into every possible space.

The industry has grown so fast factories are in all sorts of unsuitable places. And even despite the disaster at Rana Plaza a month ago, despite the statement of good intentions by companies, factory owners and manufacturers, the operation of sweat shops that break the rules is an open secret.

Read: Rescuers end search for Dhaka survivors as death toll reaches 1,127

Bosses don't want you to know, they certainly do not want you to see. But today, ITV News filmed behind the factory gates where we saw hundreds of people working in appalling conditions.

We took our camera into a complex we had been told housed some of the worst places. And we saw hundreds and hundreds of workers crammed into sweatshops. The deafening rattle of sewing machines was impossible to escape. Many workers looked far younger than the legal age at which people are allowed to work, 18.

There were more than a thousand workers in five different sweatshops squeezed into one decrepit building. What's more, factory managers told us they knew the conditions there broke the law. They did not want us to film and would not admit that on camera.

They had good reason to try to hide what is happening there.

The President of the wealthy and powerful Garment Manufacturers' Association, Mohammed Atique Islam, admitted that owners 'Of course, they do break the rules.' He said since Rana Plaza owners have been working hard to try to improve standards, and that new rules will be introduced.

Right now there are only 18 government safety inspectors monitoring factories, there will soon be 200 he promises. But there is a limit to what they can do he says, "we are not the police".

Yet many here are also suspicious about how much real appetite for change there is. Many powerful factory owners have political links - the government's commitments to change things is yet to be proved and many doubt whether they will deliver.

British brands do not deal directly with the kind of sweat shops we saw today. The difficulty for Western retailers is that sometimes Bangladeshi manufacturers subcontract their work.

Many firms try to make sure this does not happen - but is hard to guarantee it does not without monitoring factories every single day.

Read: Firms back Bangladesh factory safety plans

Meanwhile the conditions for garment workers can be awful. We met 12 year old Khalida who lives in a Dhaka slum.

Like thousands of other underage workers she left her home and parents in the countryside in search of a living. She is paid just twenty five pounds a month.

The warren of slums is a ramshackle tangle of corrugated iron huts, hardly a building. There is no running water, but rain drenches everything when it comes.

Yet she likes her life, and her job, but told me she was scared. Khalida spotted cracks in the wall in the factory where she works. She said her boss was repairing it, but now does not feel safe at work.

Not every factory in Bangladesh is the same. But many Western retailers rely on an industry where standards are often violated, and intensely difficult to guarantee.

Watch: Dhaka families wait for promised compensation

Pictures: Queues for aid parcels in Dhaka after factory tragedy