Help - my garden is water logged!

maybe dig a pond in the lowest point and the dirt you dig out will become dry

Clay soil has poor drainage at the best of times, I imagine that having built an extension you have further compacted the surrounding area.
I have heavy clay soil and when I moved in 2 years ago I had the same problem.
I dug over the whole garden to a depth of 18 inches, added multi purpose compost, grit and plenty of manure. I then left it over winter for the frost to help break it down.
Also used a hollow tine to aerate the grass area then raked sharp sand into the holes to add drainage.
Took me the best part of a week overall, but worth it as I no longer get any lying water..

Fleurdemai is absolutely right - follow his advice and you wont go wrong. Organic matter (compost/manure etc) is the recognised panacea for drainage problems - but you'll need lots of it!!

im not wrong either

No you're not wrong either NP ;-) A pond & bog garden would be just a good a way forward - always best to go WITH nature rather than try to tame her...

Thank you everyone for your help. Unfortunately it is us who have the ditch as we dug up the path so that will be my first job to fill that in. we were also thinking of getting the garden levelled as it is all over the place which should help. Yes the areas that are flooded are obviously the ditch but also the area just around the patio where the workmen were walking a lot so the ground has definitely been trodden down. Most of the garden is grass so i take it that i will just need to keep going over this with a hollow tine and add sand, but hopefully i will start to work on the flower beds when the weather improves. In reference to a pond i will have to leave that suggestion as i have three young children and i don't want any accidents - maybe when they're older!. Thanks for all your help. does anyone know anything about french drains?

...ok Jo - remember to keep off the grass and compacted bits when they are wet (difficult with kids I know) as that will compact them further. Re the French drains question - you might like to ask that as a 'new' question, as other members are more likely to see it then. Good luck :-)

nice one if u can put some crushed hard core in some of the ditch that would help to and cover in soil etc

gunnera would be lovley