A research assistant at Bournemouth University speculated that the spheres might have been "marine invertebrate eggs". The eggs can be transmitted on birds' feet and while the fall happened out of season, he noted that the winter had been mild.
While this suggestion is feasible I have a sneaking memory from similar cases reported in my youth of plane toilet disposal systems. Modern planes are, according to Wikipedia and Yahoo! Answers (the font of unimpeachable legitimate knowledge) fitted with waste systems which capture everything on the ground, but older planes were fitted with chemical toilets. Such chemicals were typically coloured blue and green and were commonly blamed for similar falls in the 70s and 80s.
Sharon Hill pointed us to this link via Twitter - the 'blue spheres' have an uncanny resemblance to Hydrogel Balls - an ornamental gardening accessory that uses gel balls as a substitute/accompaniment to soil for aesthetic effect.
Obviously one shouldn't accept any "explanation" without proper supporting evidence, but there are now 3 reasonable contenders for identifying the spheres before one leaps to any alien-centred theories. Which is a pity, cos the idea of aliens in Bournemouth is delicious.