Knock through stone wall

[Fred]

It sounds as if the existing state of the wall is a prime consideration here.  I'd be inclined to get a professional round to have a look.  If it's fairly sound and you already have a suitable piece of timber for a lintel and are prepared to get rid of the stone yourself,  it probably wouldn't take a pro more than 1-2 days.  I know a builder who'd be good for the project if you decide to follow that route.
Brian

Thanks Brian, yes I could get the materials needed and could get rid of the stone no problem. I'll have a word with you when we meet