Can i put a conservatory on the front of my house?

i have loads of space in the front of my 1960s bungalow to put a conservatory the whole length of it faces the cul de sac we live in and both the front door and back door are on the front elevation we are about 5 metres from the service road. ive read that you don't need planning permission but it says it must be 20m from the nearest highway?