Must she though?? I'm not sure we actually have an offence of accessory after the fact anymore in this country and the nearest I can find (assisting an offender) requires a positive act rather than just a failure to say anything, as does perverting the course of justice. There is also an offence of concealing an offence, but that requires payment of some sort. I suppose the money he gave her for a holiday could amount to that, but it would be difficult to prove that that was the purpose. Was there anything in her early statements that was identified at trial or appeal as a deliberate lie?
Maybe NGB could help us out here, it'd be interesting to find out what the actual position would be.
I am sorry it has taken me so long to respond to your question. I will try to deal with the key points and then apply that to Julie Mugford's position.
It is true that there the terms accessory before/after the fact are no longer used in English law (I say English rather than British or UK because I do not know if Scottish or Northern Irish law still uses the old terms). These terms were replaced with the crime of aiding and abetting the principal offender in the commission of the crime. Someone who aids and abets the principal is guilty of the same offence as the principal and is subject to the same penalties. Law students are still taught the old case law on accessories as it still applies to aiding and abetting.
In addition to the possibilty of prosecution for the main offence, someone who aids and abets may be guilty of other specific crimes, such as perverting the course of justice or assisting an offender. Knowledge of an offence does not in itself amount to a criminal offence, nor does silence save in certain specific statutory cases, such as terrorism and money laundering. To be guilty there must be some positive assistance, whether that assistance was before the commission of the offence, during the commission of the offence or after.
In the present case Julie Mugford was at severe risk of being prosecuted for several serious offences, apart from the ones she specifically confessed to, namely the burglary at the Osea caravan park, the cheque frauds and the importation and supplying of drugs (for which she would have received a prison sentence and had her career as a teacher wrecked before it began). The more serious offences were murder, perverting the course of justice and assisting an offender. If she is to be believed (and she cannot have it both ways), by her own admission she not only knew of Jeremy's plans for a considerable period before the murders, but also she provided sleeping tablets to Jeremy in order that he could see whether drugging his family as part of the murder plot was a viable option. The fact that it was not viable does not make any difference. On the day itself she was made aware that the murders were to take place but did not so much as protest, let alone take any steps which might have thwarted the plan. If she is to be believed, Julie Mugford must have been in support of what was about to happen. Further assistance was provided after the murders by expressing calming words to Jeremy during the 3.00/3.30 am telephone call. When she arrived at WHF she provided comfort and encouragement to Jeremy in the knowledge of what he had done and this assisted Jeremy in his successful efforts to present himself to the police in a way which supported the proposition that Shela was responsible. When interviewed by the police she gave an account to the police which backed up Jeremy's account. Saying nothing is not an offence. However saying something which does not include accurate details (for example of her conversations with Jeremy over the previous 24 hours) was providing positive assistance to Jeremy.
In case there is any misunderstanding I am not suggesting that I believe Julie Mugford's testimony. However, the police did and on that basis she was at extreme risk of being charged with a very serious offence in addition to the ones to which she confessed. The fear of that prosecution was in my view the major factor in persuading Julie Mugford to tell the police, eventually, what they wanted to hear. She was trapped. There was no turning back. If she did not cooperate she was faced with the prospect of standing trial alongside Jeremy, facing a substantial prison term. She did not come forward voluntarily. She was in fact arrested and held in custody for a period and subjected to intense pressure. The consent of the Director of Public Prosecutions had to be obtained to take the exceptional course of granting her immunity from prosecution in relation to
all offences (with not even a formal caution, contrary to what was suggested at trial, meaning she had no criminal record whatsoever), upon the basis of her agreeing to be a prosecution witness. It is a very sorry story indeed.