disney_cjd, If I'm grasping your gripe here - and I think I do - I believe you are mistakenly thinking all ticket prices in August > £700, and all ticket prices in April are approx £340. This simply isn't the case. To understand this, you need to get your head around the rather unique way airlines price their product.
It is unique because in most other situations when a vendor sells the exact same product they tend to sell it at the exact same price to everybody. In the world of airline seats, although the product is the same (and let's just look at the economy cabin for the sake of simplicity, but it applies to all cabins), the price will vary depending on how far in advance you bought the ticket, the restrictions on changes and - quite importantly - availability.
You may have seen lots of comments on V-Flyer about buckets, class codes, etc. For instance, codes Y, B, L, M, Q & X are all in Economy. None of those codes guarantee you a better seat, better view or better meal - in fact if you purchase a full-fare Y economy seat, there's absolutely nothing to stop you ending up in the middle of the centre section while passengers on an discounted X class are looking out of the windows with a spare seat next to them. However, as you probably realise, there is a huge difference in price across those classes - for exactly the same product. In fact, looking at the fare info on Expert Flyer for a flight out on 8th Aug for a week to MCO, I can see that the Y class fare is £1050, and the X class is £387.
The way to think of buckets is that they're like those Russian dolls. If there are seats available, all of those will be available at the full fare price, but as you work your way down, fewer and fewer are made available in the discounted class codes. Because most people buy on price rather than on the fare restrictions, the number of seats in the lower buckets go first, so when you're looking at a very popular route at a very popular time of year, the chances are that all the cheap availability has already gone. There are inevitably going to be some seasonal changes, and looking at a flight in April, Expert Flyer shows the cheapest X class at £117, but the Y fare is still £1050. In this case it makes sense for Virgin to put in special offer pricing because it's off peak, and they have to work harder to fill the planes.
There is a 'full fare' (in this case £1050) for that flight, and diminishing availability of discounts from that full fare price. The fact you're only seeing > £800 available just means the cheapest tickets have already been snapped up, not that Virgin are scalping customers just because that's the only time they can fly.
My advice is either to book at the earliest opportunity (and booking through Virgin Holidays will generally allow you to jump the gun on the normal 336 days rule, as they have a pre-allocation at an agreed rate, which is normally close to the cheapest available bucket); or change your dates to fly when the availability of buckets better suits your budget. In a world where airlines and charter operators are struggling to survive, I'm not sure it's a wise idea to chase after the carrier that doesn't maintain sensible revenue management.