There are limits to the height of things you can grow on boundaries - 6' for fences and hedges. What you could do, since you garden is long, is erect 3m or 4m high posts about 2 or 3metres inside you boundary and attach either trellis panels to support climbers or else cross bars to support a fan trained hedge on sticks. This involves trees such as beech, hornbeam and such and then training their upper branches horizontally along the struts.
The perspective from your garden will mean their height blocks out the neighbours without depriving them of light and should also give you privacy from your bedrooms and bathroom.
This picture shows a pair of parallel hedges on stilts at Chelsea last year - http://s211.photobucket.com/user/Obelixx_be/media/1205%20Chelsea%20Flower%20Show/BG43.jpg.html?sort=2&o=21#/user/Obelixx_be/media/1205%20Chelsea%20Flower%20Show/BG43.jpg.html?sort=2&o=21&_suid=136750080930500913589798526277
You could underplant with anything you fancy and make a work area behind for things like compost bins, shed etc or just make a path so you can get all the way round for maintenance.
Another alternative is to build a pergola across the width of your garden at the bottom and about 3m high and then clothe it with climbers such as roses, clematis, honeysuckle so that when you're in the garden you can't be overlooked.