[AnneB]

I was given a loganberry cutting by a plot neighbour last year.
I stuck it in a very large pot and it has grown very well.  Lots of flowers on last year's stem, but the leaves at the end are not looking quite right.
Some are coloured dark red and others have the wrong shape and are mottled.
Leaves at the bottom and this year's growth look normal.
Any thoughts as to what this could be. Viral infection?

[New shoot]

I am not sure what that is, but maybe prune out the affected stems and see if it comes back.

If that means cutting it all down to the top of the compost I would do.  You will lose the fruit for this year, but it should grow new stems for next year and hopefully they will be OK.

[Yorkie]

Have you been feeding it and, if so, with what? Just in case it's hungry too

[AnneB]

Have you been feeding it and, if so, with what? Just in case it's hungry too

I potted it on into its current pot at the end of March into new compost.  It shouldn't be short of nutrients, but I will try and give it a boost.  I do suspect a virus though.