Failed to return BPR after getting IRL

Hi all,

I received the IRL decision by end of March and received the new BRP card in the beginning of April 2019. However, I completely forgot to return back the old BRP, and now I am so worried that I may have the problem, and I am planning to return it back immediately. They warned that those who fail to return may deal with a fine of 1000, but the home office did not state clearly how long after we receive the IRL card we have to return the old card). Should I be worried about this? The second question is I am confusing to which address to send it back? In my decision letter, it said it shoudl be sent to P.O box 194, Bristol, BS20 1BT. However, my colleague who just received IRL was advised from home office to return it to 5th floor Lunar House, 40 Wellesley Road, Croydon CR9 2BY. Which address should I send then?

Many thanks for your help. Looking forward to hearing from you.

Send it to the address in your letter.