It's okay, but I didn't find it very special.
Some nice lines and observations, e.g.:

Mrs Post put her small hair combings out of the window – London birds, she had read, were short of nest-building materials.

Some dialogues that are hilarious in their inanity:

'I thought the chicken wasn't half bad,' said Mr Osmond.
'There is so much chicken nowadays,' Mrs Palfrey complained. 'Once it was a treat.'
'Oh, I agree there.'
'Variety becomes more and more important as one gets older. There don't seem to be enough animals and birds.'
'Yes, lamb on Sunday, and it's round again in three. I agree with you. Only three animals, really.'
'Of course, there's veal, but...'

But the book takes a rather glum view of old age, and of the human condition in general, it seems to me &ndash and has little to offer beyond a rather generic grin-and-bear-it acceptance of the inevitable:

As she waited for prunes, Mrs Palfrey considered the day ahead. The morning was to be filled in quite nicely; but the afternoon and evening made a long stretch. I must not wish my life away, she told herself; but she knew that, as she got older, she looked at her watch more often, and that it was always earlier than she had thought it would be. When she was young, it had always been later.

This isn't relieved by anything like the black humour with which Kinsley Amis spiced up his Ending Up, written about the same time. Nor is it taken to its bleakest extreme: there's a rather soft storyline about the elderly Mrs Palfrey meeting up with a young aspiring novelist who does his writing in Harrods – possibly inspired by the author's catching a glimpse of the young Paul Bailey working in Harrods, as Bailey explains in his introduction he sometimes privately fancied. This (very plausible) fancy gives it some literary-historical value.

This storyline might also be seen as turning this slight novella into a variation on Henry James' famous story The Middle Years, where a dying author meets a young admirer who relieves his final days with the comfort of his admiration. (Okay, it's a little far-fetched. But there are some similarities.)

This text has received lamentable copy editing, if any. Vintage should be ashamed of releasing a book literally riddled with typos (most of them clearly OCR-based) like this:

Mrs Burton felt as if she were swimming along the corridor towards her bedroom, glancing off the wails (sic) like a balloon, gliding past pairs of shoes put out to be cleaned.