Westmorland and Lonsdale MP Tim Farron has apologised for breaching parliament's code of conduct.
The Parliamentary Commissioner for Standards found he failed to register four donations, of around £56,000 in total, within the 28-day time limit.
Three of the donations were made by Faith in Public, an organisation Mr Farron has said he set up to promote his work on issues including homelessness, refugees and faith in politics.
The first donation, of £14,400 for the services of a public relations company, was accepted on 1 March 2020 and registered on 19 February 2021.
The second donation, of £22,918 for the services of two policy advisers, was accepted on 1 April 2020 and registered on 19 February 2021.
The third donation, of £11,368 for the services of an intern, was accepted on 1 September 2020 and registered on 19 February 2021.
The final donation came from The Refugee, Asylum and Migration Policy Project, with a value of £7,584 for the services of a policy adviser. It was accepted on 1 January 2021 and registered on 19 February 2021.
In his response to the Standards Commissioner, Mr Farron accepted the breaches of the rules and said he will "undertake every effort to ensure this does not happen again."
He also issued a further statement: "There are a couple of organisations that provide me with staff to help me with parliamentary work to help me serve my constituency here in the South Lakes.“Parliamentary rules mean that I have to make a declaration every year, even if the staff do not change.“I have made 2020’s declarations but unfortunately I made it late as they were due during the pandemic when me and my team were totally focused with helping thousands of local residents here in the South Lakes, during a massively uncertain time.“As a result we simply lost track of when the declarations had been made up to and when they needed renewing.“I hold my hands up and apologise for this mistake and I will endeavour to make sure that I keep my declarations up to date as I have done throughout my time as an MP."