Wanting to list a site which there's a very similar site listed here

I need to list a walking tours site of which there's a very similarly named one on your except with a .co.uk suffix, which is saying pretty much the same thing as I want to list. Is this likely to cause any problems

In general, not as long as they are different and you don't own both of them.

There are a great many categories full of sites with very similar content, but each is unique, which is one of our main criteria in choosing sites to list.

For example, almost all sites for medical clinics have the same features: details of the physician(s), opening hours, contact details, patient information forms, perhaps testimonials or photographs etc. But if they are about different practices, they are unique.

The sorts of sites we don't want to list are clearly explained here: Sites Generally Not Included.