Hello, sadly new build gardens have most opf the topsoil taken away and your left with clay and subsoil, you could put drainage in, if you decide to create flower beds in the garden, then it would be worth while getting a mini skip in and digging out the areas you want for planting and incorporate some decent topsoil from a local supplier and add plenty of organic compost over the years, is your garden on a slight slope, if so work out the areas that are likely to be always wet, anyway back to the picture, you could level it and put a membrane down, gravel it and put some nice pots of various sizes along the gravel and plant to your choice, put a climber or two in along the back on some nice chunky trellis, you could extend the border this way if you so wished, julien.

Firstly can you identify the cause of this? Which area are you in as its been so dry in parts of Britain? Could it be run off from a higher property or from a long drive on a slope? Or do you have a leaking underground pipe?
But if it is just from water not draining then it does need some serious drainage as it will only get much worse in winter. One system a friend used under her garden/lawn was gravel and french drains.

That looks like a serious problem - is your house built on a flood plain?

Mine gets like this in some areas because of the clay. I ended up digging down two spade depths and like Julien said i added a few tonne of quality topsoil/manure and stone to try and break it up a little.. I also dug 3 4ft holes in each border at the front and half filled with stone, i have hostas growing on top of them now..