Yes, frequently, particularly in the past couple of years.

Whenever I obtain a quote I make a 'screendump' of the/their final indicated price at that moment in time so that I have some evidence to throw back at them when, as you say, you find they've hiked the price upwards next time you revisit their site/that quote! When poresented with that 'original price', and their 'promise' that that price was guaranteed for 60-days, they usually concede/honour it. If not I walk...

...also find when using the sites that throw up 70/80 prices some of the figures are guaranteed up until to the date that I've given as when i want insurance to start, some only just for the remainder of the day you sought the quote.

All insurer's, in my opinion, are, how can I put this... ...but unfortunately a necessary evil.

Always, always play them at their own game. Never surrender, etc. repeat to fade...

Yesterday I started the annual process of obtaining car insurance quotes and was delighted with the first quote which was over £120 (41%) cheaper than my renewal quote (like for like) I then found three other insurers offering similar prices.

Today I decided to accept the earliest quote only to find the company concerned prices it’s policies in ‘real time’. My low quote from yesterday had in 24 hours jumped from £196 to £256. Has anyone else had this experience?

Yes.

When you visit a website and go back later you will find prices creep up, by a lot sometimes to take advantage of return visitors.

If you are going to do that clear your cookies so that the insurer does not know you have searched before.

There have been many articles about this in the financial pages. google it and be surprised.