Article 17 for the UK/Australia double taxation agreement, relates to pensions, but it does not mention lump sum payments in any way.
This means lump sum payments are not covered by the agreement:
UK/ AUSTRALIA DOUBLE TAXATION CONVENTION
As they are not covered by the agreement, it means the lump sum payment from the Australian Superannuation Fund, is taxable in both Australia and the UK.
To avoid double taxation, you can claim a foreign tax credit relief in the foreign section of a self assessment tax return, for up to 100% of the tax paid in Australia, so that you do not pay tax twice on the lump sum.