I am looking to take up my old Lawn as it has had it. it was laid by so called proffesionals and just hasn't lasted the course. Part of my new lawn will be put over to a play area for my grandson you know the sort of thing Slide swings etc.

Does anyone know of a good seed that I could use for this purpose and when the best time of year would be to sow it.

You will need a hard wearing seed blend such as British Seed House 24 blend. Lots of the courser rye grasses and plenty of bents. Any reliable seeds man will be able to supply this.
Sow mid March-late May when soil has dried out a bit and feels warm to touch.

A play area will always ruin your lawn, you may be wasting your time redoing it.Plan your garden so you can enjoy your grandchildren playing and still look at a nice lawn.
Is your garden in the shade(Large trees etc. ) as this will stop your lawn developing.
I suggest if you are going to go ahead with renewing it then wait until April and treat the existing and remaining grass with weed and feed -gets rid of any moss and weeds , then sow a hard wearing grade of grass seed( you can get this at any garden centre),about 10 days later but you will have to stop anyone using the area.will take about 2 weeks to show and will need to be a whole season to establish.
Is it possible to keep the play area separate and put down a rubber matting ground cover and rope off the lawn to protect it.

When a lawn is going to be subject to heavy use,such as a play area,a good hard-wearing grass seed mix is essential.Look for a mix including Cynosurus cristatus,Crested Dogtail.
this will be less close growing than many finer mixes,requiring less mowing.
The optimum times for seed sowing in the UK are March and April in the South,April and May in the Midlands and North.Be aware that grass does not grow well in shady conditions,requiring
constant attention.

Use a good quality grass seed that has Rye grass in it, as it will be tougher than plain lawn seed, and will stand up to playing.

I think that you should sow, around end of March-April, then the ground will have warmed up, and the seed will germinate.
Don't forget to water well every night.