Sainsbury's figures expected to hold up while TalkTalk prepares for further hack update

The supermarket, run by chief executive Mike Coupe, is forecast to post a pre-tax profit down 22% to £293 million, with margins weakening as the industry has seen prices fall for more than a year.

The Big Four supermarkets - Tesco, Asda, Morrisons and Sainsbury's - have been squeezed amid a fierce price war as they fight back against the increasing popularity of discounters such as Aldi and Lidl.

By contrast, last Thursday Morrisons posted like-for-like sales that fell 2.6%, excluding fuel, in its third quarter to November 1, a steeper slide than the 2.4% decline seen in the previous three months.

Morrisons said the slide came as it continued to cut back on promotional vouchers.

At Sainsbury's, some brokers had feared the supermarket would be in for a tough time, expecting it would bear the brunt of an anticipated revival at Tesco.

Shore Capital analyst Clive Black said: "Mike Coupe's business remains relatively resilient, particularly to any commercial challenge from a recovering Tesco."

Tesco chief executive Dave Lewis has embarked on a shake-up of Britain's biggest supermarket since taking over a year ago following sliding sales under predecessor Philip Clarke.

Mr Lewis has closed failing stores and sold off non-core businesses in bid to boost its key UK operation, and brokers had feared Sainsbury's more upmarket offering would be the most vulnerable of the major supermarkets to a resurgent Tesco.

But Sainsbury's was the only one of the major supermarkets to see sales rise by 1.1% to 16.1% market share in the 12 weeks to October 11, according to the latest till roll figures from respected research group Kantar Worldpanel.

Sales were boosted by a strong performance at its online operation and its convenience stores.

Mr Coupe said in June he saw little sign of an end to falling prices.

He said: ''We will see price deflation continue until the end of this year, and into next year. This is good news for customers but puts pressure on our sales.''

Mr Coupe, who took over from long-standing predecessor Justin King last July, unveiled a wide-ranging plan to fight back against the discounters in November which included price cuts to 1,100 items and improvements in quality to 3,000 own-brand products.

He pledged to spend £150 million on cutting prices under the plans.

The supermarket said last year that a quarter of its stores have under-used space and over the next five years this will be used for concession partnerships and to expand its non-food offer.

Sainsbury's opened three Argos concession stores during its first quarter - in North Cheam, Nantwich and West Hove - adding it plans to open 10 by the end of the first half of its financial year.

Telecoms group TalkTalk is expected to update the City on the impact on sales and customer numbers at its interim results on Wednesday in the wake of last month's hack attack.

Analysts at Citi said the firm will cancel its interim dividend and suspend its financial guidance until it can get a full grip on the hack on its computer systems.

On Friday TalkTalk said the details of 156,959 customers and 15,656 bank account numbers were accessed in its recent cyber attack.

But it emphasised the "information accessed cannot on its own lead to financial loss".

This is a lot less than the firm had first feared. It had earlier said it may have lost the personal details of up to 1.2 million customers as well as up to 21,000 bank account numbers and up to 28,000 obscured credit and debit card details.

The firm said last month it will only waive termination fees for customers wanting to end their contracts if money is stolen from them.

However, brokers at Citi estimate the impact of the bad publicity and the suspension of its website, which is a key means of selling products to customers, will see it lose around 200,000 accounts by the end of the full-year, leaving it with 4.1 million customers.

The City forecasts the business will turn in half-year earnings of between £90 million and £95 million, around 16% lower than a year ago.

In recent weeks three teenage boys and a 20-year-old man have been arrested by the police in connection with the alleged data theft from TalkTalk.

This is the third time that data from TalkTalk had been hacked in the last 12 months, and chief executive Dido Harding will have to answer critics who have called the attack relatively unsophisticated.

Investors expect to see further signs of improvement in the key markets of telecoms giant Vodafone when it posts its half year results on Tuesday.

The City forecasts interim group earnings will slip 3.2% to £5.69 billion, but expects to see service revenues rise by 0.9% as the group begins to see sales rise in key European market offsetting slowing growth in India and South Africa.

This will build on results in its first three months of the year in May when it reported its first quarterly revenue growth in nearly three years as conditions improve in many southern and western European markets.

The mobile phone giant saw a 0.1% rise in service revenues in the three months to March 31, with the UK up 0.6% after returning to growth in the previous quarter.

In the UK, growing demand for 4G services and the benefits of its £19 billion Project Spring investment plan contributed to the best half yearly revenues performance since early 2012.

Shareholders will also want to know about the firm's acquisition ambitions after the firm said in September that talks with UK-based cable firm Liberty Global over a potential asset swap had collapsed.

Back in June, the telecoms giant entered discussions with Liberty regarding ''a possible exchange of selected assets between the two companies''.

There had even been speculation that the two were considering a merger that would have created a £100 billion telecoms giant, but Vodafone dismissed such talk.

But analysts at JP Morgan said: "We suspect the saga is far from over given the strong strategic rationale for a deal, in an increasingly convergent world."