We were reluctant sellers of our notional holdings in Avon Rubber last week when its share price finally triggered a sell signal under our stop loss system.

The shares had been hovering on the brink for the past few weeks as a result of selling by nervous investors following the abrupt departure of chief executive Rob Rennie after little more than a year in the job.

The company says trading in products ranging from military gas masks to teats for milking machines continues in line with expectations and no fewer than three stockbroking firms believe the shares are now some 20 per cent undervalued.

But we make it a rule to eject virtually all share tips which have fallen 10 per cent from previous peaks.

Only New Year selections enjoy a temporary reprieve to allow for a three month settling in period.

The disposal crystallised a loss of just more than £100 for the 2014 portfolio which has also hit by a fall in the price of supermarkets group William Morrison after it warned on the trading outlook for 2017.

Happily, these losses were more than balanced by gains in the other four tips in the portfolio which was showing an overall gain of around 1 per cent when we carried out our weekly review of progress on Friday morning.

The other portfolios fared less well with all three recording losses over the week as a result of sharp falls in one or two shares following disappointing trading news.

The 2017 list was particularly hard hit by a slide in the price of Glasgow’s Aggreko power plant group and saw a 2.3 per cent fall in its total value despite small gains among the other selections.

Shares in the Scottish company slumped 14 per cent at one time after chief executive Chris Weston warned of the likelihood of lower profits in 2017 as a result of weak oil markets and problems in Argentina.

The scale of the setback means that Aggreko is facing eviction from the portfolio when the stop loss rule finally comes into play on April 1 although the company has maintained its generous dividend as a sign of conconfidence in the future.

The 2015 portfolio suffered from a markdown of Renewi –the old Shanks waste treatment group—to show a fall of around 2 per cent and the 2016 selections gave up 1 per cent of their total value following profit taking in model trains group Hornby.