Oh dear, this is getting further and further away from being accurate. Dealing correctly with capital allowances, let alone dealing optimally with capital allowances is way way beyond the scope of what can be discussed here.
"if you choose to defer claiming capital allowances then you cannot subsequently claim them if you no longer own the asset. So if in ten years time you have scrapped the assets or sold it or given it away then you cannot claim for it."
This is not true. The cost of the asset (less any disposal proceeds) will remain as part of the General Pool on which Writing Down Allowances may be claimed.
"You should claim the AIA in the year you buy the asset as the relief is currnetly 100% ie in effect its treated as an expense (unless you subsequently sell it) who knows what the treatment will be in future years."
But for a self employed person with income below the Class 4 NI threshold there is no point in claiming AIA.
"And it would be hideously complicated trying to keep track of unclaimed assets or expensive to do (if you use an accountant)."
No it isn't - as part of each year's tax computation you deal with each asset purchase, either claiming AIA (or FYA if available) or adding to the General Pool, Special Pool or treating otherwise as appropriate.
"If claiming the tax relief makes you lose money then
a) you don;t have to pay corporation tax this year"
b) you may be able to claim you losses back 12 months if you made a profit last year and get an immediate refund of some of last years corporation tax
c) if you didn't make a profit last year or this year then why are you in business! then you carry your losses forward and get automatic tax relief on the first year you do make tax and any subsequent year until you use up all your losses."
The OP is a sole trader. Claiming the tax relief wouldn't make him lose money, it would simply reduce his profits within the nil rate income tax/Class 4 NI band.