Lawn grass identification

Hi evryone

I was wondering if anyone can help identify what type of grass my lawn is.

There is a patch of grass which I have been told is couch grass, it's got quite thick stems and has a purple tinge to it, having also dug up a small patch I can confirm it has long white and quite thick roots as far a grass goes. I have started to dig this out and will treat as I go.

Having looked at the rest of the lawn I'm thinking is it best for me to kill the whole thing and start from scratch.

Im not sure what other grass is growing in my garden.

Any help is appreciated.