To ask this in here but can anyone recommend something quick and easy to remove dead flys and general road dirt please? It's for my work car that spends its whole life on the motorway so I just need something quick and easy to use and it's constantly dirty.

Cheers,

A jetwash.

A quick detailer should do if doing it on the hop when your out and about or a spray of diluted degreaser or all purpose cleaner prior to washing will soften and loosen the bugs so they'll wash off easier. 

Though a good wash and seal will go along way into making it easier in the future to keep clean. If your not all that into washing the car or don't have a lot of time to, try Gyeon Wetcoat or CarPro Hydro2. Wash the car properly the first time, thoroughly rinse off any shampoo and then (without drying) haphazardly spray one of these products over the car and pressure rinse the car again. Your car is now protected and super easy to keep clean with just a quick shampoo or just a pressure wash. Repeat as and when after six-ten weeks and job done.