The clifftop bar overlooking the Aegean Sea was perfect. Set under a trellised vine on a tiny square in front of a domed, whitewashed church, it seemed the ideal place for a sunset aperitif.

I ordered a glass of wine and sat back to enjoy the golden light and thudding of the waves hundreds of feet below.

‘Excuse me, are you waiting for someone?’, asked the waiter. ‘Er, no. It’s just me.’ ‘Oh… are you sure you want to sit there, lady?’

He spoke politely enough, but his expression was belligerent. I glanced around quickly: there were hardly any other customers on this late September evening, but clearly he wasn’t happy.

Then I understood my mistake – the table I had chosen, its bench spread with charming vintage cushions, was for two. I was taking up too much room.

I gathered my book and my bag and scuttled off apologetically to a stool in the corner. As the sun went down and the bar slowly filled up with couples, I struggled to stop myself bursting into tears. Night one of the worst holiday of my life.

Until this last visit to the small Cycladic island of Sifnos, I’d always loved travelling alone.

I was a happy member of the growing group of solo female travellers whose bookings, new data suggests, have risen by 20 per cent in the past two years.

Far from being a daunting prospect, going it alone is increasingly appealing for many women, and I understand why. In my 20s, I had travelled alone in Asia and Central America, but after I married, holidays became very much family affairs.

Then, as a divorced single mother for many years, I had always chosen child-friendly destinations. After my daughter left for university, I relished the opportunity to go back to pleasing no one but myself.

I happily explored the Pacific Coast of Mexico, Morocco and many of my beloved Greek islands, entirely alone and entirely content.

Being free to choose where I went and what and when I ate, and to spend all day on the beach with a novel or get up at 6am to do yoga without consulting anyone else, was a glorious kind of selfishness.

My Italian husband always preferred the same traditional destinations he had grown up going to – Sardinia in the summer, Switzerland in the winter – which grew a bit stale.

Post-divorce, holidays became marvellously liberating.

But this trip – my first solo holiday since turning 50 – was different. Frankly, I felt old and lonely.

Of course, being able to spend ten days on a Greek island is a huge luxury, but that somehow made it worse. Not only did I feel isolated and sad, I felt guilty about it. Why wasn’t I able to enjoy a morning swim or a wander round the fascinating little archaeological museum?

Being single had never bothered me before, but now I had to admit it: I felt wretched about not having a partner.

Everyone on the island seemed to be half of a couple except me. I was painfully conscious of the odd pitying look as I sat alone night after night, although it wasn’t even the lack of romance that was upsetting me. I was just sick of hauling my heavy suitcase up steep, cobbled lanes; wrestling with ferry timetables on my own; and having no one to go sightseeing or share a coffee with.

After a few days, I felt like Pauline Collins in the film Shirley Valentine when she makes friends with a rock.

I also began to feel like a terrible cliche: the lonely English woman looking for love in the Mediterranean. Taking a taxi from the port, the driver asked me if I was married. When I said no, he asked if I’d like to join him in the front seat or meet up for a nighttime excursion to a mountain monastery.

Costas was no Adonis – he had fewer teeth than strands in his combover – but he clearly felt he was in with a chance. It was the sort of chat-up I would once have laughed off, but now it depressed me. Did I look that desperate? Clearly, the answer was yes. Another evening, I had chosen a beautiful garden restaurant in the island’s main village, Apollonia. When I gave my name for the reservation, the waitress frowned and checked it was for one before leading me to a small table next to the loos.

I asked if I could move, and she explained that unfortunately they were fully booked. Wine, I was informed, was only available by the bottle. Fine, I’d take a bottle of red, drink what I felt like having and put the cork in to take back for another night.

‘A whole bottle?’ she repeated, in a voice that would have been loud enough to be embarrassing if the restaurant had in fact been fully booked. I wanted to say a defiant ‘Yes’, and ask her to bring me an ouzo on the side while she was at it.

Instead, I found myself babbling that I wasn’t a heavy drinker, that the wine would probably last me three nights, and didn’t she agree a glass of red would be just the thing with the sirloin steak I planned to order? My reaction would have been funny if there had been anyone to share the joke with, but instead I just felt humiliated. ‘The steak’s for two,’ she said bluntly.

Instead of a treat, dinner became an ordeal – practically every menu seemed to be for sharing. I felt conspicuous and ridiculously nervous, under-ordering in case I seemed greedy, over-tipping to compensate for the inconvenience of taking up a table.

I hated myself for it and told myself I was being ridiculous, but in the end I gave up and took to eating dinner in my rented studio with dismal supplies gleaned from the mini-market, which seemed even more pathetic.

I’ve read a lot about how women experience a sense of ‘invisibility’ at 50, but – perhaps arrogantly – I hadn’t expected it to happen to me. I have always been reasonably confident about my looks, but that self-assurance evaporated on Sifnos. I became almost paranoid, sidelined and acutely conscious of slights at every turn. Without a man by my side I felt belittled, as though I had experienced a sudden drop in status.

Obviously, I’m not as physically attractive as when I cheerfully and recklessly hitchhiked my way round Vietnam at 25, yet the wisdom of maturity cut no ice on the island.

Accepting this change was difficult. The independence which feminism encourages is, of course, a good thing, but I think there is also a pressure for women in their 50s to insist that we’re just fine; that of course we can traverse the globe alone, savouring new experiences without the whims and demands of a partner tying us down.

We’re not allowed to admit that it’s hard, or to own up to the truth that we might not all be happily single. I have been mostly single for ten years now, but this was the first time it stung.

Those ten days on Sifnos diminished me, but they forced me to be more honest with myself, too, which can only be a good thing.

I can admit without apology that I’m feeling more timid as I enter my 50s. I’m not quite ready to book a Saga cruise, but the next time I plan a trip I’ll definitely do it with friends.