Parents are lobbying for a change in admission rules in South Gloucestershire schools to prevent brothers and sisters being split up.

At one school, families whose older children are pupils have been told their younger siblings will have to go elsewhere because there isn't enough room.

They have been caught by the rule that says only families living within two miles of a school get extra priority for having children already there.

In Acton Turville, near Badminton, that means some parents who do not even live in South Gloucestershire are allowed a place because their home is closer.

The village is not far from the county border so families in Burton and Nettleton – both in Wiltshire – have been granted places for their children at Trinity, while parents in South Gloucestershire areas that are slightly further away cannot get their children accepted.

Now those families affected by the rule have launched a petition for a change in what they claim is an unfair system.

They said it will leave them with major difficulties getting their children to lessons in the morning and collecting them in the afternoon from schools that are often miles apart.

The mums and dads have also enlisted the support of Northavon MP Steve Webb, who is backing their efforts, and said: "Under the present rule, only families living within two miles of a school get extra priority for having children already there.

"There are some families who have no children at the school at the moment but because they live slightly nearer, have been awarded places, including parents who do not live in South Gloucestershire."

The families want the council to change its admission rules so that having siblings at Trinity carries increased weight, no matter where they live.

Sharon Taylor, 38, of West Littleton, has 10-year-old Jake and six-year-old Libby at Trinity but when four-year-old Isabella starts school in September, she will have to go to Marshfield Primary.

Sharon said: "The distance we will have to cover is a problem if we are to get the children to two different schools at the same time."

She also wants Isabella at the same school so she will be with her siblings.

Belinda Delargy, of Hinton, has one son, Charles, at Trinity but his brother, Harry, will have to go to Wick Primary when he starts school in the autumn.

She said: "The schools are in opposite directions and about nine miles apart.

"To drop both children at 8.45am at two different schools and collecting them both at 3.20pm will be impossible."

South Gloucestershire Council spokesman Ryan Skeets said 90 per cent of those applying for a school place for this year got their first preference, with 96 per cent allocated one at one of their preferred schools.

He said: "Siblings are given a high priority when allocating places if a family lives within a certain distance of the school or where the family live in an Area of Prime Responsibility for a particular school or schools.

"The council also has to take into account a legal ruling which would make it unlawful for an authority to treat applicants living outside the local authority area less favourably than those living within it.

"The council reviews and consults on its school admissions policy annually and considers any responses to the consultation before the policy is agreed.

"These issues were not raised during the consultation for September 2009 and September 2010 admissions.

"The views expressed in any petition can be fed into the consultation process for the September 2011 admissions policy."