liquid fertiliser and weed kill for lawn

My mother's back garden, about 1/2 acre is in poor condition. Was sown out about 4 years ago but I reckon the grass seed was poor quality. Anyone recommend a good all round liquid fertiliser, moss and weed kill which could be applied with a garden back sprayer?

Any other thoughts also greatly appreciated. Thanks

In B&Q I always buy feed&weed, you can get it liquid or seed form, works perfectly for me on my front and back garden.

I think the combination moss/weed killer and fertiliser treatments are only recommended to be used from April due as the gaps created in the lawn by killing weed and moss cannot easily be filled in by grass re-growth earlier. I used a granular fertiliser before which I bought in B&Q, think its a chicken manure based one, but it can be applied by sprinkling on both in late autumn and from early spring.

typical blame the grass seed... it could be poor soil fertility and if there is moss incorrect ph levels or and perhaps it was sown too late/early in the year and weeds got ahea of the grass and grass seed never got a chance. get a product called mortox it will take care of your weed problem too earlyto spray yet though, use iron sulphate to sort out the moss it will take a few appliciations though, get some granlime to improve the ph balance and make it harder for moss to grow. stop cutting the grass so low sunlight getting to the bare soil drives the moss on. if there are bare patches rough it up and mix in some moss peat and spread some more seed..