Scottish Gas has come under pressure to cut its energy bills after parent company Centrica announced inflation-busting profits in the first six months of this year.
Unseasonably cold weather in the spring and early summer helped British Gas, which trades as Scottish Gas north of the border, to increase its profits by 23% from January to June 2012.
The company's 16 million energy accounts brought in almost £2m a day as total gas consumption rose by 3.5%.
Shadow energy minister Tom Greatrex told STV News that energy companies should explain why savings in the energy sector did not appear to be passed on to customers.
British Gas warned in May that bills could go up this winter because of rising wholesale gas costs. Since then wholesale prices have fallen.
The Labour MP for Hamilton West said: "Why is it that when costs go up the bills go up like a rocket, and why is it that when costs come down, the bills come down like a feather?
"That's a real issue that people and consumers across the whole of the country are right to be concerned about and it needs to be addressed."
In reply, British Gas said in a statement: "We continue to take the lead in our commitment to make energy choices simple, transparent and fair for all of our customers, helping to drive long-term growth."
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