The 52-year-old presenter fell while preparing for a pentathlon event in aid of the charity PiggyBankKids, founded by Sarah Brown, wife of former prime minister Gordon Brown.
Last night a spokewoman for ITV said: “Lorraine was doing normal training when she fell off her horse in south London. She’s not broken anything and is just bruised.
“She’s being kept in hospital overnight as a precaution.”
Mrs Brown, president of PiggyBankKids, said: “Our thoughts are with Lorraine as she recuperates. She’s such a good friend of PiggyBankKids and we would like to thank her for the contribution she has made and wish her a speedy recovery.”
Ms Kelly, awarded an OBE in the 2012 New Year Honours for services to charity and the armed services, is a novice rider and has been preparing for the charity event with fellow learner Mrs Brown.
The competition at the end of February at Pentathlon GB’s High Performance Centre at the University of Bath involves completing a small course of jumps on a horse as well as a 3km run, with stops every 1km to shoot at targets with a laser hand gun, fencing and a 200m swim.