jeepers, that must've taken you a while to type ruthandsam lol ;-)
Right-ho,
You obviously don't need any more weight lifting exercise as you are working in a very active role and are currently gaining muscle - however, as you are also gaining non-muscular weight, it's time to start thinking about some light cardio exercise and changing your diet pattern slightly. Your fluid intake is good (no sugar, no caffeine) your diet is good in the mornings, but starts to waver slightly later on in the evening(?) but having no sweet things is also good.
I used to have the typical apple shape, so was advised to cut down on the amount of white bread, sugar, pasta and cheese I was eating then upped the amount of lean protein, Vegetables, eggs, full fat milk, and high fibre complex carbohydrates such as brown rice and beans and the weight soon dropped off (but I haven't lost my muscles as I'm outdoorsy too)
I would try and graze your food throughout the day (swap the bread and crisps for a chicken salad or tuna with light mayonnaise on a seeded bread such as 'Burgen' and low fat thick yoghurt) as this can stop any hunger, then have your main meal with a fist sized piece of lean protein and more vegetables than you can shake a stick at to fill you up. Have plenty of healthy nibbles ready to grab so you don't spoon out another portion of dinner later on.
After work, before your OH gets home, go for a nice brisk walk (if you have a dog all the better) to get some cardio in for 1/2 an hour each evening (or in the morning if you are an early bird) - or how about checking in at the swimming pool for a few lengths on the way home from work?
Probably try and eat fruits with less fructose if possible (dried fruit in the nuts? pears, apples and grapes, blueberries) and eat more low fructose fruits: Plums (already, good), peach, strawberry's, apricots, melon, banana - as fructose can cause an immediate blood sugar spike which in time can lead to insulin resistance (which in turn will trigger the fat storage metabolism).
As Eve has mentioned - might be worth taking a trip to the doc's just to ensure there are no underlying factors which might be contributing to your weight gain.
Don't be tempted to resent your muscle build up as the more muscle you have, the more energy your body burns even in a relaxed state. And lastly - don't beat yourself up about having gained weight full stop. You are in a fantastic out-door job and are more than likely fitter and healthier than ever before (?) But if it is getting you down, a few small changes like the suggestions above will help over time, you don't need to enrol in a gym or starve yourself to do it - just enjoy life and up yer cardio, protein and veg ;-)
I have no doubt that everyone's diet opinions on here will be different, just choose the options that fit into your day-to-day the best