What's causing the brown patches? Do you have a dog?

i'd get in touch with the landscapers. are there any large rocks/drains in the grass areas that are brown ?

and do you have a dog or rabbit that wee's in these places. [my eldest rabbit does scorch the grass when she wees. grrr!]

Also, how have you been watering it? It takes some skill and patience to water a lawn effectively just holding the hosepipe. I usually recommend investing in a sprinkler head that you can set down on the yard. You don't have to leave it long in each spot, but it will water far more evenly than the untrained eye and twitchy hand.

Thank you for all you responses, but they do not resolve the problem of how to get the brown patches green again.
I do not have any animals that could go on the garden at all. Will speak to the landscaper and ask his advice.

Angela, if it is a kind of grass that forms rhizomes, such as bluegrass, it may come up from the turf once the problem that caused it to turn brown is resolved. In any case, the problem that caused the browning must be ended, before you can sow seed or lay new turf.
My suggestion is that you may have accidentally caused the browning by unknowingly watering unevenly. Given a deep, even soaking, the brown areas might green up again, if it is the right species of turf. Other possibilities are fungus diseases, from watering too often--I would be surprised if new turf in the UK needed watering more often than once every two days. New turf only needs it once a day here, in the hot desert. If fungus is the problem, then it will have to be dealt with before green grass can grow If there is something under the brown spots stopping root growth, then that will need to be removed before new turf is laid, or seed is sown. Since it is the front lawn, it might not be your animals that are causing problems. Again, the animals need to be stopped, if you hope to avoid more brown patches.
There, all laid out, is what we can tell you about greening your grass. Not likely to be any effortless fixes, sadly.

Posting a photo or two with a little more background information would really be helpful to determine the source of your brown patches.