UK based question

Ladies, how long after your midwife refers you do you get an appointment through the post for your dating scan/downs syndrome/pataus/edwards? My midwife referred me and said that they generally tend to want to do the tests around 11 weeks so i should get a letter in the post fairly soon (im 8w5d today) but im just so antsy and keep running to the post everyday!

I know no one can give me an exact timeframe but i just wanna know if other ladies were in the same situation as me, did they end up having to wait a good week or two?

Thanks in advance lovelies xxx