Form 11 & Top Slicing Relief

Hi everyone,
I am about to complete my Form 11 for 2008 on ros and I see a section for Top Slicing Relief in the employment section. It says "Amount of Top Slicing Relief claimed in 2008". I presume that I can calculate the TSR due to me for redundancy in 2008 and enter it here. That way I wont have to write to revenue and wait for them to do it.

If anyone can tell me exactly how to calculate TSR I would appreciate it.
For the prior 3 years I presume I add up the Net Tax Liability and Taxable Income for each of the 3 years from my completed Form 11's and divide them to get the average. Or is it the average rate for the 3 years employment only ( just PAYE income and not including other income as the Form 11 would do ).

After that its straight forward.
Thanks,
blarney

The lump sum ( after deduction of any exempt amount) is taxed at the rate obtained by dividing the Total tax payable for the three years of assessment immediately prior, by the taxable income of those three years ( if this is lower than the rate it would normally fall to be taxed at as income in the year of receipt.

So this would be total income as per Form 11, not just the Paye income and tax thereon.