if you're 30 and living in 'the country' your insurance shouldn't be too bad. dont mind the cc of the moped or bike - your licence i think should cover you more on power to weight. (i.e. you could probably get insured on a 1300cc hardley style bike but couldn't get insured on a honda 400 cc CBR type race style bike) i haven't been on a bike in about three years but i drove them before that for about six years - to and from work every day. from what i can remember i'd advise as follows:
dont buy a two stroke;
not sure where newcastle is - is it down beyond wicklow or out near blanch somewhere ??? - if you have a long drive each day buy something that is comfortable to sit on - and offers good cover from the wind and rain - i.e. something with a front fairing and a good sized screen;
if you're not a bike enthusiast and just want something for getting from A to B i'd suggest one of the bigger style 4 stroke 'mopeds' - like a 250cc etc - they would have the advantage of not destroying your shoes with changing gears and they have room under the seat for a lock, wet gear - lunch or whatever few bits you need to bring to work.
i drove more performance style motorbikes and, given my age and location, i could not afford fully comp insurance so i only had third party only - i.e. if the bike was stolen i didn't get a penny from the insurance company - so just check out where you live, who safe you think it is, and where you would be leaving the bike in work and consider what type of insurance you can afford or need - also the nicer the bike the more attractive it will be to the scum-bags out there.
if you dont like the idea of a moped, a good starter bike would probably be (very cheap) an old import honda bros 400 or, if you've a few more quid to spare - and this would be much more comfortable - something like a honda deuville or maybe one of those bmw gs650s - you have the advantage of sitting up higher in traffic and seeing further ahead with the latter two.
good luck ! you have me itching to sell the car and get back onto a real machine now you swine!!
edit - sorry just read your original post again - ignore the stuff about motorbikes so - i'd suggest a four stroke moped, either a 125 or a 250cc - depending on your drive - if you go on motorway type roads or big dual carraige ways - go for the 250 - shouldn't make much difference in price or insurance. check out things like a suzuki burghman - i cant remember the yamaha equivalent - MCN (motorcycle news) has a good website and might be worth a look for reviews etc.