Supermarket Morrisons looks set for an 11th hour reprieve from being booted out of London's blue chip index thanks to a shares rally after enjoying its first sales rise for nearly 18 months.

The Bradford-based chain was on track for an embarrassing exit from the FTSE 100 - ending more than 14 years in the top flight - after a tumultuous time for the group had seen its share price tumble.

The relegation was due as part of the quarterly FTSE reshuffle, which was based on last night's closing share prices.

But Morrisons saw its shares leap 2 per cent higher yesterday after industry figures from Kantar Worldpanel revealed sales edged 0.1 per cent higher in the 12 weeks to May 24 - the grocer's first rise since December 2013 and the only sales growth among the Big Four supermarkets.

The rise lifted Morrisons' market value to £4.04 billion, a whisker above mobile power company Aggreko's £3.99bn worth, which is now likely to see the supermarket cling on to its place in the top tier.

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The FTSE results of the shake-up will be confirmed after market close later today, when the FTSE committee meets to make the final decision.

While modest, the sales growth provides a welcome boost to Morrisons' new boss David Potts as he prepares to face shareholders at the supermarket's annual general meeting on Thursday.

Experts said the sales figures suggested the turnaround at Morrisons was beginning to gain traction and shares were up more than 2 per cent again today.

Shares were also more than 1 per cent higher for listed rivals Sainsbury's and Tesco as the Kantar figures signalled a narrowing in deflation, which has been putting the squeeze on grocery profits.

The data revealed food deflation stood at 1.9 per cent in the three months to May 24 - a reversal of the previous trend, which had seen the rate deepen to 2.1 per cent.

Analysts at Bernstein said the narrowing in deflation was reversing the "longstanding decline since November 2011" and showed the first signs of inflation turning the corner.

Shore Capital's Clive Black said: "Grocery stocks are through the worst of their travails as structural change takes place."

But yesterday's market share data made for painful reading for the major players.

Morrisons held its market share at 10.9 per cent, while its main rivals Tesco and Asda suffered falls as they continued to come under pressure from discounters Aldi and Lidl.

Tesco's market share dropped to 28.6 per cent in the 12 weeks, down from 29 per cent a year earlier, as sales fell 1.3 per cent while Asda saw its share fall to 16.6 per cent from 17.1 per cent after a 2.4% sales slide.

Sainsbury's maintained its share at 16.5% despite a 0.3% fall in sales, according to Kantar.

With Morrisons the only one of the top four to enjoy an increase, Kantar said its fightback was gathering pace.

Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel, said: "A committed core of loyal Morrisons consumers is responding positively to recent initiatives and business has been boosted by online sales."

But he added: "Morrisons' performance is an improvement on what was a difficult May 2014, so this is only the first step in any future recovery."

Mr Potts took the helm in March, replacing Dalton Philips, who was ousted in January after sliding profits and sales.

Thursday's annual meeting will be watched with keen interest after last year's AGM saw Mr Philips submitted to a humiliating dressing-down in front of shareholders by former chairman Sir Ken Morrison.

Sir Ken described Mr Philips's strategy as "bullshit", as the then-boss faced intense pressure amid sliding sales and a fierce supermarket price war.

It is expected that Sir Ken will be in attendance at this year's Bradford-based meeting, with other family members, who are thought likely to vent their anger at the £2.1 million paid to Mr Philips last year, plus a £1.1 million pay-off.