Power of assessment: Best judgement: Lack of information
You may encounter difficulty when trying to make an assessment to best judgement.
If a business is unable or unwilling to provide all the information you would like or has not kept comprehensive records, you would be fully justified in raising an assessment.
This may include higher range estimates, see Spillane v HMC&E 1990 STC 212.
If the amount of the assessment is disputed then the onus is on the business to disprove the assessment, perhaps by providing further information or reconstructing its records.
In the Van Boeckel case the High Court held that although the Commissioners had to exercise their judgement as to the amount of the assessment in a reasonable manner, they were under no obligation to do the work of the taxpayer by carrying out exhaustive investigations.
In a colourful analysis on the same theme, the High Court in the Schlumberger Inland Services Inc.  STC 228 case considered that, where a business provides only the minimum of information to the Commissioners, the officer raising the assessment
‘… is not required to possess and deploy the deductive powers of Sherlock Holmes and the clairvoyance of Madam Arcarti provided that the assessment raised is not in excess of what could reasonably be payable.’