As a resident of Canada, you need to declare your world wide income, which would include the income your earned from this UK savings account.

The Canadian tax system does provide a foreign tax credit for any foreign tax you may have paid on this income to the UK such that you generally aren't double taxed on the same amount of income.

To enter this amount, go to Foreign Slip (found in the T-slips section), Enter the income in Canadian dollars and also make sure you enter the Country such that the foreign tax credit would be calculated.

Do I need to declare that in the Foreign Slip as well as in the T1135 slip?

If the cost of all your foreign assets is more than $100K, then yes you would need to include this income on the T1135.

Turbo tax specialist are telling me I don't need to fill the T1135 slip, if I haven't received it. Is that correct?

Assuming the cost of ALL your foreign assets is more than $100K, then you do need to file a T1135.

Here is additional information that may be helpful:
https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents/information-been-mo...

Thanks, it looks like I was given the wrong info then.
I see filling the T1135 doesn't automatically fill the Foreign Slip,so I have to fill both.
But I think if I declare in the Foreign slip the Foreign taxes already paid abroad, then I don't need to add again this info in the Foreign Tax Credit or Foreign Tax Paid slips, even if that amount doesn't show in the last 2 slips.
My foreign assets are in countries that have a tax treaty with Canada, to avoid double taxation.

Yes, that's correct. If you have added your foreign income and foreign tax paid in the Foreign Slip (and make sure there is a country entered in Foreign Slip), then you don't need to add the amounts into Foreign Tax Credit.

Thanks!