It drives me crazy that Google Chrome keeps trying to correct my spelling to American. Here’s what to do if it annoys you too!
Click on the 3 bars at the top right of the browser window, and then choose Settings, then at the bottom click on Show Advanced Settings. Under Languages choose Languages and spell checker settings. Now, English will probably be on the list already, but ignore this, and click the Add button, and then select English (UK) from the drop down menu and click OK, You then go back to the previous window, where you must click on Display Google Chrome in this Language, and Use this Language for spell checking. Finally, click Done (or OK) then close and re-start Chrome. Hopefully from now on, your emails will be checked for English UK spelling, not American!