This service is provided by The Royal British Legion, in support of the Poppy Appeal Registered Charity No 219279.
The mobile operators give the following % of the donation to the Legion:

On Orange and Vodafone the Poppy Appeal will receive 100% of the £1.50, £3.00 or £5.00 donation.
On 3 and T-Mobile 75% of the donation goes to the Poppy Appeal and 90% of the donation on O2.