as fooman says, risk, if you can afford the risk ie your mortgage is £500 a month but you can easily afford to pay £1k, then go for a tracker as unlimited payments, if you can only afford the £500 then get the fix..
mortgages need to be paid down to 65% LTV to ensure you get the best rates available, if your mortage ltv is high then you’ll get poor rates. my first mortgage was a lifetime tracker, which kept dropping from 2008.
hsbc
2 year fix (65%ltv) 4.54% [versus 4.29% £999 booking fee
Tracker 2 year is 6.09% [ie tracker is 0.84% above curent 5.25%.] fee free unlimited overpayments.
is the base rate gonna fall 1.55% in the short term, i doubt it,
i’d only take the tracker if i wanted the flexibility to pay it off in full, but then you could lump sum before fix starts
otherwise SVR is 6.99% for full flexibility. need to also consider if you intend to move or get divorced in the fixed timeframe, and or ease of switching