Is this space big enough for a downstairs toilet?

[Springmachine]

The space available is 1150mm x 1120mm

Would that be suitable for a downstairs toilet ? The door can open outwards so we don't need to worry about door opening space

I'd use a corner toilet. That should work. Might be a bit tight for knee room otherwise even with a compact toilet.

You can get toilets with a washbasin topping the cistern, the handwash water drains into the cistern, so saves space and recycles some of the water. Genius.

www.bathshop321.com/p2-combination-toilet-and-sink/?gclid=EAIaIQobChMIs5O3lJaC4AIVB6maCh3M3gO0EAQYByABEgIlTfD_BwE

I have one in a tiny house which has been carved out of the under the steps to the front door bit. 120 cm x 110 cm & sloping ceiling . It works - separate loo and v slim tiny basin but it works - practical . I reckon with an outwards opening door - you could do that.

If you look on Pinterest for tiny cloakrooms/understairs toilets you can get lots of ideas.

Our entire en-suite is 90cm wide by 245cm long

We used this sink unit as it’s the narrowest we found
www.ikea.com/gb/en/products/washstands-taps/wash-stands/lillången-washbasin-cabinet-with-2-doors-white-spr-19188035/

It's totally doable.
nendengi.club/wp-content/uploads/2018/03/bathroom-under-stairs-tiny-bathroom-under-stairs-design-bathroom-under-stairs-ideas.jpg

www.houzz.co.uk/photo/2534390-refurbishment-of-1930s-semi-modern-bathroom