Connect outdoor aerial where wire aerial is?

I have a new home hi-fi system, a (UK) Times newspaper offer (manufacturer anonymous). It's my first new one for years, and I was surprised to find there's nowhere to connect an outdoor aerial; only one of those wire aerials coming out through the back, kept in place with a knot.

I'm in Ireland, and can only really get BBC radio with a big, external VHF aerial, (however good the radio). (The aerial's inside, to be pedantic, but we have a high enough ceiling, and a susceptibility to lightning!)

The Times offers helpline was sympathetic, but said that's how they all seem to come these days. They warned that opening the case myself might invalidate the guarantee.
I'm not too bothered about that - I've tested all the functions and they all work well - reception's the only problem.

The co-ax cable from the proper aerial already goes to our hi-fi position - it just needs joining up to the new system, if it's possible. I'm used to fiddling around inside computers, radios etc (though just self-taught), and am familiar with the precautions involved. If it can't be done by simply making the wire aerial outside the case connect with the co-ax, I won't have a problem unscrewing the back to get further in.

I'd be grateful to hear from anyone who's done this!