I have been asked to clone some existing software for a company. Basically its an old 16 bit DOS console app, which was supplied free of charge in I believe the late 80's. Having replaced the machine that needs to run it with a box running Win7 x64 they can't get it to work. It crashes every couple of minutes under DOSbox.

The company that supplied it appears to no longer exist - if they did the company asking me to do this would almost certainly know about it. Its undetermined whether they have gone entirely or are just trading under a different name. If the latter they seem to have withdrawn from the market related to this product (because again, niche area, we should know about everyone there).

What is the status to this with regards to copyright etc.? The main concern for the company involved is they want an identical interface to what they already have so I would have to clone this entirely. Having no source code / indication of the underlying mechanisms these would be written from scratch.

Is an interface covered by copyright? / Does that still hold 30 years later? What is the assumed license when none at all is provided?

Under UK law would I be under any serious risk were I to take on the project? How would this pan out if I then decided to sell the software on to other companies?

Thanks