Not sure how big that area is but my first inclination is to dig it up, level it, rake it smooth and lay rolls of new turf.

Is it a shady area?

The full lot is about 38m2. It was 45m2 but I keep reducing it with Borders. It does have some shade throughout the day from a large tree and hedges but is south facing so does get some sunlight. I thought about digging it over but gardener said to reseed it. Not sure what I should do?

It really is your choice. Its just that I find turf a more reliable way of doing it but choose a week when it's not hot and ideally when rain is forecast because new turf will suffer in the heat unless you are very careful and it will need regular watering for quite some time too.

The same is true for seed.

I think we are going to go with the seed option. It'll be back braking to re-turf and we were quoted £500 for a professional to do it! I'm going to weed it tomorrow, cut it, spread topsoil and the rake in seed. We'll see how it goes :O)

If it gets less than 4 hours of sun a day, you may want to look for shade tolerant grasses, such as Roughstalk Bluegrass (Poa trivialis), or Tall Fescue.

Many thanks Tugbrethil, I'll take a look at those. I should really time how much sunlight it gets!

Thoroughly investigating the garden's sun exposures is one of those details that are so helpful to the gardener, and so rarely done.