I think Jeremy may have been worried that BT might have been able to prove that he made a telephone call from White House to Goldhanger and that nobody picked up(the answerphone message would be activated),so he made a call to Julie first upon return to Bourtree Cottage and then telephoned Witham,where he either hung up after one or two rings or didn't telephone them at all,and only at that stage did he telephone Chelmsford Police Station. At no stage did he dial 999 which he was worried if he did they might have been able to trace the preceding call,and it also gave him time to clean himself up(this has been called the "Radox" moment thoughI've forgotten who mentioned it)whilst he was pretending to flick through Yellow Pages for the Chelmsford number.