Indian Passport extension query while on tier 2 general visa

Hi All,
I am applying for my passport renewal next week at vfs edinburgh and I am submitting the documents as mentioned below

1.Current passport
2. Original BRP card
3. Photocopies of passport first page , last page and expired visa pages (self-attested)
4. Photocopy of BRP card (self- attested)
5. 4 photos. (4 PHOTOS 2”X2” REQUIRED.)
6. Fee : £ 52.00
7. Original Marriage certificate and photo copy of Marriage certificate Self-attested by me and my wife [as i am going to include my wife's name in my new passport]
8. Spouse original passport
9. Original spouse BRP card
10. Photocopies of spouse passport first page , last page and expired visa pages (self-attested)
11. Photocopy of spouse BRP card (self- attested)


I have one question to clarify as mentioned below

I have bought 2 small royal mail Special delivery covers weight upto 150 grams to receive my original docs and my new passport..is that ok???? or
do I need to buy 2 big royal mail Special delivery covers of size A4 And weight upto 500 grams


please clarify on this...
Thanks and Regards,
scher.

if passport is going to be posted back to you, then you need to provide them with 500g special delivery envelope.

Why don't you use the courier service provided at the VFS centre itself?