Hello and welcome to the forum.
PJP this maker’s mark is unknown to me. You could try and ask;
The.Library@thegoldsmiths.co.uk
All they need is the same image,the people of the Library Goldsmiths .Co are friendly and very helpful.
As for the date; beginning in 1975, date letters became standardized in all of the operating assay offices across the United Kingdom. As of 2000 the use of a date letter is voluntary.
The official voluntary date letter for the year 2000 is the letter
a. I believe the cross with 2000 denotes the year 2000. The world celebrates the start of a new millennium, approximately 2000 years after the birth of Jesus who died at the cross.
Oel