The UK's main share index briefly passed the 5,600 barrier for the first time in four years on Friday.
Friday was a quiet day on the stock exchange
Yet in a quiet half day of trading that ended for Christmas at 1230 GMT, the FTSE 100 eventually finished down 2 points to 5,595.
Analysts said the shares slipped back due to a lack of corporate news. Marks & Spencer was one of the main risers.
The London Stock Exchange will now reopen for trading after Christmas on Wednesday, December 28.
Shares in Marks and Spencer gained as investors are confident the retailer has had a strong Christmas trading period.
Drugs giant AstraZeneca was another riser after it said it was buying Cambridge-based cancer treatment research firm Kudos Pharmaceuticals for around £121m.