Can anyone tell me why our pears are brown inside this year?

You may simply have waited too long to harvest them this year - the majority of pear varieties should be picked before they're obviously ripe, because they ripen from the inside out, so if left too long, the flesh in the centre starts to rot, working its way outwards until the whole thing looks rotten on the outside.

Thank you Bamboo. That is probably the reason then. The tree has got so tall now that we couldn't reach them and had to wait for someone younger to get up the tree to reach them!!!! :))
Such a shame.

Do you know if we can prune it to make it smaller in future?

This was a tree from a Comice pear pip.
I planted it years ago and didn't expect to get any decent pears, because you never know what you will get from planting pips do you, but they have been really lovely and very similar to Comice. (the only pears I like!!)

Not my area of expertise, pruning fruit trees, but from what I do know, I think the tree should have been trained from a young age to keep it small, especially one you've grown from a pip. Fruit trees grown from pips obviously are growing on their own roots rather than from a rootstock - the usual rootstock for pears is quince, and that keeps the tree at up to 2.5 metres max, whereas one grown from a pip, well its anybody's guess how tall it might get eventually. Some info about fruit tree pruning in the link below,not sure how much help it'll be

https://www.rhs.org.uk/advice/profile?PID=858

Many thanks Bamboo, I will look it up.