I understand now how to create negative numbers in brackets and have attempted to save the style as a new style in the style box but it seems that when you come to use Excel on another day, that style has not been saved by the program and you have to start again. I have resorted to copying and pasting from other spreadsheets to obtain the same effect. Why is this happening and what am I doing wrong?

Hi David,

Thank you for the post, you may be doing nothing wrong, if you have followed the right steps for creating a style it should be available in that workbook until you delete it.
Just in case you are missing a step I will put the sequence in here:
To create a style that will automatically format these cells for you, follow these steps:

Click on one of the cells in your worksheet.

Go to Format>Style.

In the Style name box, type (for example) Total cell.

Click Modify.

Under the Number tab, select your required style, you say with negative numbers in brackets (this may be also be a custom format.)

To add some borders etc; under the Border Tab, select Single Line under Line styles and click the Top Border button on the menu to the left.

Select the Double Line under Line styles, then click the Bottom Border button. on the left.

Click OK twice.

If you then want to format a Particular cell/cells, select the cell/s and go to Format>Style, choose Total Cell from the drop-down list and click OK.

This feature won't save you much time if you have to do it for every workbook. Luckily, you can copy the style to any other workbook by following these steps:

Open the workbook that contains the already defined style.

Open the workbook to where you would like to copy the style.

In the workbook where you want to copy the style, go to Format>Style. Click Merge.

Select the other open workbook from the list and click OK.

Has that helped? regards Pete