ST27 - I've been running for over 20 years and can't ever imagine not training - it is part of me & I hate rest days! (I actually prefer training as races make me very nervous)
Definitely worth keeping a log of your training & the following which most have suggested will add a bit of 'spice' to your training 
Vary the length and intensity of your routes; vary the terrain you run on; Be adventurous - run a really scenic route and leave the watch at home; introduce running into your commute, lunchbreak or visit to family; Mix in some speedplay (fartlek) or faster bursts/pickups; Vary the time of day you train; Introduce some cross training; have a running break or holiday - doesnt have to be abroad, can be somewhere in UK e.g. Lake District, Dorset.
I dont think there is anyway you can approach a marathon and be realisitc about completing it unless you get the training runs in...also races aren't really cheap these days - surely you want to get the best race result you can and run to your potential?
I hope these ideas help (I'm speaking from experience here - I've suffered more than my share of motivational dips in the past) Enjoy and dont fear experimenting or adding variety to your training.
Good luck!