sillyquestion wrote:If I want to apply for BC upon return to UK, I will have to stay in UK for 5 years under ILR status to qualify for BC?
No, this is incorrect, you are not required to have held ILR status for 5 years.
sillyquestion wrote:Is it possible to apply for BC straight away after 5 years of Tier 1 General visa? Or Do I have to apply for ILR and then wait for 12 months before applying for BC?
No. Yes, you will need to wait 12 months if your spouse/partner is not a BC.
The following explanation may help...
Once you are granted ILR as a T1G economic migrant, you will be free from immigration time restrictions and can leave and return as you please, so long as you have not been away continuously for over 2 years and are returning with the intent of settling in the UK permanently (As vinny has pointed out, there are exceptions to this requirement, but they do not apply to you from the information you have provided). Your ILR status is not meant to be used as a visit visa, where you are settled in another country and coming to the UK for short periods of time.
The standard residential requirements for BC after you are granted ILR are as follows:
To demonstrate the residential requirements for naturalisation, you must have:
a) been resident in the UK for at least five years (this is known as the residential qualifying period); and
b) been present in the UK five years before the date of your application; and
c) not spent more than 450 days outside the UK during the five-year period; and
d) not spent more than 90 days outside the UK in the last 12 months of the five-year period; and
e) not been in breach of the Immigration Rules at any stage during the five-year period. and
f) You must be free from immigration time restrictions (i.e. have ILR) when you apply for naturalisation. Unless you are married to or the civil partner of a British citizen, you should have been free from immigration time restrictions during the last 12 months of the residential qualifying period.
In your circumstances (where you were granted ILR as a T1G Migrant) this would mean you would be eligible to apply for naturalisation 1 year from the date you were granted ILR, so long as you meet the absence thresholds mentioned above and all other requirements for Naturalisation.