Sitting not sat!

English has unfortunately for foreign learners a simple tense and a continuous tense.

Simple present I sit Continuous present I am sitting
Simple past I sat Continuous past I was sitting.

We use the continuous tenses much more than the simple ones, as in I am sitting writing this right now, or I am sitting at my desk. However, if we always do something, we usually use the simple tense. I always sit here, where the continuous tense is used of something we were doing or are doing as we speak: I was taking a bath when the phone rang.

In standard RP English, mischievous is pronounced something like ‘MISchiffus ‘, with iistress on first syllable.

Sorry. I don’t know where ‘iistress’ came from.

Sounds like a bit of Hylda Baker, " sat sitting here waiting ".
Nelly Pledge--Nearest and Dearest.

Perhaps people who say conshume and ashume have been at the Baileys!