Older passport /travel information for UK visitor visa

[tigercov]

My uncle needs to apply for UK visitor visa and one of the requirements is provide last 10 years travel details.

The current passport was issued in September 2007 and expires in 2017. The older passport number is printed on the back page along with date of issue which was valid from 1997 to 2007. There was another one before this but the problem we're facing is we seem to have lost both of the older passport or misplaced it as we moved house.

Now that my uncle want to apply for UK visitor visa using online application form - it requires to submit information - for example, "Do you have another passport or travel document?" If I answer Yes, it asks for passport number, place of issue, date of issue, date of expiry. (I filled in the one from 1997 to 2007)

The the application asks again if we have another older passport and its details but We don't know the details.

Can you please advise if we should answer NO as we don't have these older passports with us?

I know sometimes immigration officers demand for older passports to be shown and we don't want to give any false information to home office. How do we tackle this situtation?

Just to mention - my uncle holds valid multiple entry Canadian visitor visa which is valid till end of 2017 and he travelled to Canada last year without any issues.