The Ryanair rostering system is designed to man all flights at the lowest possible cost to the company. This is why there seems to be no logical distribution behind your roster.
Another reason why UK based pilots are not flying as much is because the market in the UK is currently saturated. Ryanair has a disproportionate amount of bases in the UK compared to other countries. There is too much passenger overlap.
To give an example. At my base in central Europe we have a passenger overlap range of roughly 350km total travel distance. This means that through airport surveys Ryanair has established that the majority of its' passengers at my base live within that distance of the airport. This equates to roughly 200 miles. Outside that radius, a passenger is more likely to choose another Ryanair base over mine as the departure point of his travels. I have these figures from by base captain, so they should be more or less accurate.
When you transmute those figures to the UK you'll see where the problem lies. All the major UK bases (Stansted, Luton, Bristol, Birmingham, East-Midlands, Leeds) are positioned on average less than 150 miles from each other.
In the UK, you have 6 bases in the passenger overlap radius equal to that of just 1 central European base. Add to that the fact that Stansted has a much larger passenger attraction rate because of the larger spectrum in available destinations. In short, the competition for passengers between UK bases in much larger than the competition for passengers in central Europe.
In my base, you'll get 1 standby per week normally. Can't speak for FO's, but captains keep averaging around 75 up to 90 hours per 28 days. From FO's I hear variable numbers, but not as low as I've read here. I would say average around 55 per month for the youngsters.
I feel for the guys flying 40 hours or less. I hope my post gives some insight in the reasons behind it.