Shares in BAE Systems boosted the London market after Qatar signed a letter of intent to buy 24 Typhoon jets from the defence company.
The deal, announced at the weekend, sent BAE shares up 2.9%.
That made BAE one of the biggest risers in the FTSE 100, with the index up 32.50 points, or 0.5%, at 7,247.97 shortly after midday.
A slight fall in the pound also helped the benchmark share index to claw back some of the ground lost last week.
Sterling had risen sharply at the end of last week after the Bank of England indicated that an interest rate rise could be on the cards before the end of the year.
But that rise had pushed share prices lower, as a stronger pound cuts the value of FTSE 100 companies’ overseas earnings when they are brought back to the UK and converted back into sterling.
However, the pound weakened slightly on Monday, dropping 0.4% against the dollar to $1.3539 and falling 0.5% against the euro to 1.1316 euros.
In the FTSE 250, shares in Esure rose 6.8% after a report that the insurer’s biggest shareholder is looking to sell.
The Sunday Times said that Sir Peter Wood, who owns 30.7% of the company, has been in talks with possible buyers of his stake, which would trigger a bid for the whole business.