Twin sisters are celebrating today after achieving 15 A and A* GCSE grades between them.

Isabella and Katharine Hay, who attend Wiltshire independent school St Mary's Calne, insist there was no sibling rivalry driving their achievements even though big sister Georgina achieved three As at A-level last week.

Isabella achieved three and a half A*s and four A grade GCSEs while Katharine gained four and a half A*s and three A grades. Both studied for a shortened form of the religious studies exam counting as half a GSCE.

It marks a week of celebration for the family who live on an organic farm near Huntly, Aberdeenshire, with all three sisters at the school.

Katharine, who is younger than Isabella by several minutes, said: "I am not surprised we got similar marks as we seem to work at the same kind of pace.

"We are both really pleased for each other. We do look quite similar but there is no sibling rivalry or jealousy. We used to be inseparable but we are branching out as we get older and have developed different interests. We are also both really close to our big sister Georgie.

"Isabella loves her languages and art and is on a French exchange at the moment while I adore drama and have just been at the Edinburgh Festival."

The twins, who also have two older brothers, will return to St Mary's Calne next month to follow in their sister's footsteps and do A-levels at the school.

Katharine added: "Eventually, I hope to do something in the drama world and Isabella would love to do something with her art, maybe architecture. In the meantime, we are both hoping that we can do as well as Georgie at A-level."

All three girls are also accomplished musicians. Georgina was a sixth form music scholar at St Mary's Calne while Isabella plays the violin in the school orchestra and string ensemble and sings and Katharine plays the piano and organ, sings and is learning the accordion as a hobby.

Their mother, Debbie, said: "We are so delighted for all three of our girls to have done so well. We will definitely be having a bit of a celebration tonight."

More than seven in 10 students scored an A*-A in their GCSEs at the school with 99% achieving A*-C Grades in all their exams.

Head of St Mary's Dr Helen Wright said: "We are delighted with this strong GCSE performance from St Mary's girls.

"We believe in personalising each girl's curriculum according to their individual strengths which has resulted in our GCSE success. We continue to develop this innovative approach to learning which sees the individual student at the heart of everything we do."