The biggest mistake is missed a general overview.
You have to write a general trend before or after main paragraph.
At a glance when we look at the table
This states overall paragraph but next you mentioned specific detail.
The table shows the percentage of electronic machines used by the British over about one decade from 1972 to 1983.
Are you sure that this table shows the percentage of electronic machines? in the table there is the percentage of households with ...
Thus, I believe you should write in the introduction:
The table compares the percentage of British's households with different electronic machines between 1972 and 1983.
In addition,it seems that you had written about used machines but not about owned.
Anyway I could be wrong, if so correct me, good luck with your Ielts exam