Simon Calder: Mediterranean mystery tour for cruisers

So you have chosen your cruise: one described on our pages perhaps, or the tempting new itinerary for P&O's Bermuda-registered Oceana for January 2012, starting in Southampton and taking in Jamaica, New Orleans and Charleston, as well as Madeira and the Azores. You study the guidebooks and decide how you will spend your day at each port of call. But don't get too excited: all cruise lines reserve the right to change destinations at short notice.

Just this week, Grand Princess and Carnival Miracle bypassed St Kitts, following the robbery at gunpoint on the island of 17 tourists on a shore excursion from Celebrity Mercury . Azamara, part of the same consortium as Celebrity, warns customers hoping to see Casablanca that "We are currently intending to visit Morocco, however due to security concerns it may be necessary for us to amend these ports of call".

(The same cruise line takes a literary liberty, inviting customers to "feel the spirit of Shakespeare's Hamlet surround you in Copenhagen's Kronberg Castle"; last time I checked, the fortress properly known as Kronborg was 27 miles north of the Danish capital.)

To call or not to call? Usually ports are missed for more mundane reasons than safety fears. On a Costa cruise from Dover to Greenock, I missed out on the Isles of Scilly – and saw quite enough of Falmouth – because of bad weather in the Atlantic.

ppp At least Falmouth is in the same country (and county) as Scilly. The Thomson Dream this summer cut out an entire continent. Passengers who boarded the Dream at Palma in July anticipated an exciting itinerary that included Barcelona, the lovely island of Menorca and Tunis in North Africa. But a sequence of misfortunes meant she missed several ports of call. Mahon, the pretty capital of Menorca, was axed because of concerns that the available tugs would not be powerful enough to manoeuvre her safely in harbour. And Barcelona, where cruise ships dock almost at the foot of the Ramblas, was deleted due to "port congestion" (the Catalan capital was hosting the World Athletics Championships). As a result, some passengers found themselves in the interesting but limited port of Tarragona twice in a fortnight.

Tunis was dropped (and replaced by Cagliari in Sardinia) because the ship's desalination plant wasn't working properly. While water could be bought at European ports, Tunis did not have enough available. This meant an aesthetic loss for passengers who had set their hearts on visiting the nearby ruins at Carthage. It was also a financial blow for the excursion organisers and souvenir sellers of Tunis. And Thomson got hit twice: cutting out the North African city meant the trip became an intra-EU cruise, removing its duty-free status; and the company gave every passenger £50 in on-board credit to make amends.

The firm says "Thomson Cruises plan future cruise schedules a long way in advance. At times, the need for an itinerary change becomes apparent close to the departure date. When this happens, we always try to notify passengers in advance but this is not always possible." The company also points out that only one in five passengers is on board for two weeks. "Whilst regrettable, our alternatives [to Barcelona] were limited and Tarragona was the best option we had available."

ppp What rights do you have, when the one place you have longed to visit is axed from the itinerary? None. Indeed, the terms and conditions of Carnival, the biggest cruise firm in the world, say that cutting ports from cruises are treated only as "minor or not significant alterations".

Lost in the Burgess Hill triangle

Trains, like cruise ships, can also miss planned ports of call. On Wednesday I set off from London to Burgess Hill in Sussex to visit what is billed as "the greenest hotel in Britain" – a brand-new Premier Inn. To travel sustainably, I took my bike by train.

Never mind Bermuda: beware the Burgess Hill triangle, an unexplained phenomenon that makes this pretty patch of Sussex almost inaccessible.

The first train was late, and missed the planned connection; the second was also delayed, and took me only as far as Hayward's Heath – two stops short. The promised next train to my final destination was, I was told, running so late that it no longer had time to stop at Burgess Hill and would run direct to Brighton.

I abandoned the bike and hailed a cab, arriving an hour late and £15 lighter. To complete the throwback to the bad old days of British Rail, my planned train home was cancelled, too.