If you look at UK history, there's a long standing tradition of anti-semitism. The secret files show1940's a plot to kill Gen Barker. Combine that with the history of colonization, and it makes sense that there was a plot to kill the commander of British forces. Starting from around the 12th century, there are recorded persecutions of Jews and discrimination. In British literary tradition, there are many references to what some scholars call "culturally embedded" antisemitism. It may not be deliberate, but it is persistent and has affected society in the UK.
Yes, the U.K. has strong anti-semitism, but this can be corrected. A lot of countries suffer from some sort of prejudice, and the U.K. is no different. It takes the educational system to improve awareness for future generations. Once anti-semitism is proven to take place, it should be wiped out with education.
Based on the U.K.'s recent release of files revealing Jewish terrorists, it is difficult to determine if they are anti-Semitic. Conducting an un-biased investigation into Jewish terrorism doesn't necessarily mean the U.K. is anti-Semitic. The release of these files could assist in understanding terrorism more and lead to many answers regarding this topic.
There are certain files that governments need to keep closed for the public's and country's safety, and suspected terrorist files would certainly be among the ones that should not be opened in haste. The decision to wait to open the files does not indicate that the U.K. bears strong anti-antisemitism.