I am about to send my 90 day by post, i live in Bangkok and i am getting conflicting info on where to send it.Is it ok to send it to the old immigration office in SuanPlu or is it better to send it to Chaeng Wattana. I am from UK .Different sites say ok to send to SP if you live in Bangkok.

The only site that matter is Thai Immigration's site where it gives the correct information and address for postal reports as Chaeng Wattana.  A UK citizen cannot submit 90 day reports to Suan Plu.

3 hours ago, tethered goat said:

Is it ok to send it to the old immigration office in SuanPlu or is it better to send it to Chaeng Wattana.

No it's not, you need to send it to Chaengwattana. There is a lot of outdated/wrong information on the net.

 

90 DAYS REGISTRATION,  
IMMIGRATION DIVISION 1
Chalermprakiat Government Complex
120 MOO 3, CHAENGWATTANA ROAD,SOI 7, 
LAKSI, BANGKOK. 10210

http://bangkok.immigration.go.th/en/base.php?page=90days