If its Grade II you will need to find a good local architect who has listed building experience and a working relationship with planners.

expect the process to take years, to be expensive to build and instead consider moving house.

@Jonathan thanks but moving wouldnt be an option. My partner owns the estate the cottage is in. The cottage is actually larger however it was divided into 2 seperate cottages years back and we rent out the other half. Feel like we are in a bit of a predicament!

If you own the estate it may be easier and cheaper to find an alternative property or plot within the grounds to develop

Hi Leah this is also probably not helpful but assuming you are unable to extend upwards or outwards, could you combine the cottages back into 1 than you would have the additional space. My sister has bought a grade II listed house and the expense it has cost them to go through planning to make simple updates is a nightmare!

Could you post picture of the upstairs space, maybe some clever space planning would work?

@chloeloves hi it is a possibility but it would only be possible if the neighbours unfortunately passed away, they are elderly and we arent prepared to tell them to move out or anything like that! and it would mean a loss of one of our incomes as well. however it may be more cost effective in the long run so definitely would consider it if that was the situation.

Maybe you could extend out to the side, no clue where your boundary is. The planners might be more sympathetic to that than something that messes with the roofline. Hope you haven’t got bats in the roof, protecting them is very £££!

I think it will be difficult. You may get away with a garden room added to the back made mostly of glass?