BORIS Johnson has been accused of lacking “leadership” by Westminster’s ethics watchdog, after he failed to maintain an accurate register of interests.

In a stinging report, Kathryn Stone criticised the cavalier attitude of the former Foreign Secretary and Tory leadership hopeful after he wrongly claimed all the facts were up to date.

In fact, the Uxbridge MP, who was reprimanded last year for failing to register financial interests, had also failed to include a part-share in a property in Somerset.

Ms Stone concluded he was almost a year late in declaring his 20 per cent stake.

Parliament’s cross-party Standards Committee also complained of “an over-casual attitude”.

Ms Stone said Mr Johnson’s repeated failures to “might be regarded as showing a lack of respect for the House’s rules and for the standards system”.

Although Mr Johnson will not be sanctioned, the report's timing is acutely embarrassing given his ambition to replace Theresa May as Prime Minister.

Mr Johnson has now apologised and accepted “full responsibility for the error”.

Ms Stone said: "I do not accept that this was an inadvertent breach of the rules.

"Mr Johnson has co-operated fully with my inquiry, but his failure to check properly that he had brought his Register entry up to date during my last inquiry might be regarded as showing a lack of respect for the House’s rules and for the standards system.

"That does not demonstrate the leadership, which one would expect of a longstanding and senior Member of the House, nor compliance with the general principles of conduct."

After considering Ms Stone's report, the Commons standards committee said: "We conclude with concern that these two investigations by the commissioner in rapid succession demonstrate a pattern of behaviour by Mr Johnson.

"While there is no suggestion that he has at any time tried deliberately to conceal the extent of his interests, this latest breach reinforces the view which we expressed in our previous report, that he has displayed 'an over-casual attitude towards obeying the rules of the House', in conjunction with 'a lack of effective organisation within [his] office'.

"We find it particularly regrettable that Mr Johnson gave an assurance to the Commissioner that his registration of financial interests was up to date, and within a very short period it proved not to be."

The committee said Mr Johnson must now meet the registrar of members’ interests to be reminded of his obligations, and would face a more serious sanction if he breaks the rules again.

Ms Stone said she had started her inquiry into Mr Johnson on her own initiative in February after finishing a previous investigation into him in November.

That found he had failed to declare nine payments worth almost £53,000, most from book royalties, within the 28-day time limit set down by parliamentary rules.

Mr Johnson apologised in the Commons after being asked by the Standards Committee.

During that inquiry, Ms Stone had asked Mr Johnson to confirm his register of financial interests was up to date, and he assured her on 24 October that it was.

However on January 17, the MP registered a new interest - a fifth share in a property in Somerset - which had arisen on October 4. This declaration was also late.

“Mr Johnson told me that he had considered registering the interest sooner but had concluded that it was not necessary to do so,” Ms Stone reported.

She concluded Mr Johnson was eleven months late in registering his share.

She said she had “no reason” to think Mr Johnson had any intention of hiding the interest, and accepted that as Foreign Secretary had less time for personal paperwork.

“Nonetheless, as a senior and long-standing Member he should have made sure that he had appropriate arrangements in place so that he could ‘ fulfil conscientiously’ the House’s rules on the registration of their financial interests. He evidently did not do so.”

She said Mr Johnson’s failure to register his book royalties “demonstrated a lack of attention to, or regard for, the House’s requirements rather than oversight or inadvertent error” and his failure to register the property might be seen “as part of the same pattern of behaviour”.

But she added: “But Mr Johnson’s failure to check his register entry properly in October 2018 before telling me that it was accurate cannot. This was a separate and additional lack of care and attention to the rules which apply to all Members of the House.”

In a letter to the Standards Committee, Mr Johnson said  “I wish to offer a full explanation as well as an apology.

“Last October my office completed a review of all payments received and confirmed that my register was up to date.

“Alas, at this stage the share in the property was not added, since I am afraid that I misinterpreted the rules. The value of my share is well below what appeared to be the threshold of £100,000, and any share in the rental income is well below £10,000.

“When in January it was drawn to my attention that the threshold in fact related to the value of all property owned - and that the barn should therefore be included - I took immediate steps to update my register.

“I accept that this should have been done as soon as the property was given to me (and my siblings), and I accept full responsibility for the error.

“Having now carefully reviewed the rules again - at the suggestion of the Commissioner - I do feel that they could be clarified so as to reduce the possibility of confusion.

“I repeat my apologies to the Committee for my inadvertent delay in registering the property, and stress that the error was rectified as soon as I became aware of it.”