From August 7 to 21, the gardens, park, adventure playground, and dinosaur trail will be free to visit for Blue Light Card holders and British Armed Forces personnel. Edward Lytton Cobbold, director of Knebworth House, said: "We know that family days out can quickly add up during the school holidays, so we hope this offer gives Blue Light Card holders and British Armed Forces personnel the opportunity to enjoy a great day out at Knebworth House with their family and friends." Summer offer thanks Blue Light and Armed Forces personnel (Image: Supplied)As part of the Blue Light and Forces Fortnight, visitors simply need to show a valid Blue Light Card or proof of British Armed Forces service at the main entrance to receive complimentary admission. Free entry scheme launches at Knebworth House (Image: Supplied)The promotion does not apply to pre-purchased tickets, which cannot be refunded or exchanged. Set on 250 acres of parkland with 28 acres of formal gardens, Knebworth House is a popular family destination in Hertfordshire, featuring a giant playground and more than 70 life-sized dinosaurs.