After having an extension built three years ago my enclosed back garden was
turfed and everything seemed perfect until about a year ago when the grass
became very patchy and seemed to recede to be replaced by large areas of
clay. It's even more galling that prior to the turfing the lawn had always
been fine.

The open plan west facing front lawn was also done slightly later but is not
suffering the same conditions.

Can anyone please suggest simple straightforward steps to return the lawn to
the grassy area it once was that my children can play on. A local small
bedding plant seller has suggested Canadian Grass Seed & sprinkling top soil
on it but the national chain round here doesn't stock it the grass seed and
has not proved to be very helpful.

Any suggestions please would be kindly received