my neighbours tree looks like this every year and all she does is pick up the leaves and in spring feeds it. she says its scab.
at this time of year I would expect it to drop its leaves and then stay dormant until spring. remove the dead leaves and bin don't compost.

see what others suggest.

I would say that there is nothing wrong. It is Autumn and the leaves are dying and will be dropping soon. Only if they looked like this in the Spring would I be concerned.

I'd have a word with the seller if I were you. Gradually turning autumnal & dropping leaves over a period is to be expected. Turning black & spotty in two weeks doesn't seem right?
I'm just over in Manchester & the leaves on both my pear trees are still dark green & hanging on despite the wind!
You didn't re-pot & bury the graft? There's something white on the trunk lower down that doesn't look right?

it looks like a wax layer to protect the graft. but take a closer look in case its woolly aphids

Looks like pear scab. I would take it back! Here is a link for identification & treatment:

https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9003.pdf

Thank you all for all the replies. You guys are so helpful. I bought the plants from Morrison’s, guess I won’t be buying plants from them again as I also bought a plum tree which has been looking rather sad (although not as poorly as the pair tree). I’ve taken a pic of the trunk (not sure how to attach) and there doesn’t seem to be any while stuff on the base anymore. Most of the leaves have fallen off now and I’m hoping the scab won’t come back in spring.

I’ve newer grown a pear tree before, can they be shaped into espalier/fans and any key tips on how to care for them?

Yes pear trees can be an espalier, but you must begin training them when they are 1 to 2 years old, they you train them along the wires. You must first start with a healthy tree that will last long enough for you to enjoy your rewards. Then read this:

Espalier Pear Tree Maintenance: How To Espalier A Pear Tree
https://www.gardeningknowhow.com/edible/fruits/pear/how-to-espalier-a-pear-tree.htm

I haven't had a problem with any plant I've bought in Morrisons. why not take a photo and take it in and ask what they think the cause is. I assume you have the label that says its from Morribobs!