Cutting 8mm hardboard

[Rupster]

I need to cut neatly into a false wall made from 8mm hardboard to improve access to my stopcock.

What would be the best kind of saw/other tool to use for this?

Thanks.

I’d score the cutting area using a knife and metal rule and then carefully use a multi tool. Little tidy up around the edges with sand paper.

Not used a multi tool before so will check out. Thanks.