On 20 October last year a senior judge granted him temporary bail to go to his brother’s wedding.
Middlebrough was permitted to first go to Liverpool and then briefly stay in West Yorkshire and was ordered to surrender to HMP Wandsworth in south London on 24 October.
He never showed up and a judge later issued a warrant for his arrest.
Police believe Middlebrough, known to friends as Shibby, was helped to leave the UK by a well-organised network of supporters.
Since his disappearance, he has sent messages to supporters, which have been published, saying he refuses to be “held as an Israeli prisoner of war in a British prison”.
Reporting of Middlebrough’s conviction was delayed because of a separate prosecution in which he and another man were accused of planning to carry out a Palestine Action-themed protest at Boris Johnson’s 2022 wedding party.
Middlebrough’s trial on that allegation has now been put back indefinitely for legal reasons.
Judge Patrick Field KC, the judge in Middlebrough’s trial over the Elbit break-in, lifted the reporting restriction on his conviction at a hearing on Monday morning.
He is the fifth Palestine Action supporter to have been convicted over the attack.
Two more trials of alleged participants are expected.
BBC News has contacted the police for comment.
