So now that I am slouching in front of a computer screen at work for most of the day

[Gingerbear]

They won't let me out on site - too risky apparently.
My back is aching and my bump is resting on the desk. I am sure the lentil weavers would frown at my lack of activity for one in a such pregnant state.
What can I do to make sure my posture is correct and more importantly help me stay fit for this pregnancy?

Make sure your chair is adjusted properly to give your back adequate support. If you are short (like me) you might need to use a footstool to keep your legs supported.

Walk around as much as you possibly can - go to the loo every hour even if you don't need to; offer to make cups of tea for everyone in the office (!); wander off to do some photocopying then remember a bit more you need to do in a few minutes' time: anything to keep active and keep your circulation going!

Do you get a long enough lunchbreak/work close enough to go swimming during the day? Great way to keep fit and active and increase your stamina for labour.

Good point Miaou - I am a shortarse so will ask for a footstool.
We have half an hour officially for lunch, but as we work flexitime, I can squeeze in a 20 minute walk.
Local aquanatal classes are helpfully at 11am, so I will start swimming in the evenings after Christmas. (Have been meaning to do this for ages!)

I swam religiously throughout my three previous pregnancies (only once a week) and I swear it really made a difference when it came to labour. I worked up to 40 lengths in under 40 minutes, then back down to 30 as I got nearer to term. Sadly I live too far from a swimming pool to do it this time round so it will have to be power walking for me!

Before DD I used to swim 3/4 times a week (Oh the joys of not requiring babysitters!) It is a great exercise for PG isn't it? no worry about muscle strain and you don't care that you look like a whale in the water.
Shame about your lack of local pool. Can't you crack the ice on a local loch?

pmsl! Er - no

They are building a pool at Craignure (Mull) - which I can see from my house (Craignure that is, not the pool)! But sadly it won't be finished in time for me to use it before this one makes an appearance - boohoo.

Craignure - I had no idea where that was, so I googled it. It looks lovely. Very touristic.
Can't you book in some training sessions with Josie Jump in Tobermory? lol.

lol at Josie Jump! I'm actually on the mainland here - the little yellow square down and to the right is Craignure - so not far away.