I tried Skyscanner initially & for the cheapest flights it always directs me to book through Opodo which reading the reviews online are a bit mixed.
I have just found a Monarch return flight from Manchester on the 23rd July with decent times, 23kg each, online check in & choose our own seats for £755 + 4.5% credit card fee.
Jet 2 all seem to be above the £800 mark, dont know wether to take a chance & hang on for the Easyjet flights which I have read will be released in October or just take the plunge with the Monarch deal