  The Standard Model Higgs potential is very likely to be metastable, in which
case Higgs Inflation is likely to require an extension in order to stabilise
the potential. Here we consider stabilisation by adding $n_{Q} \leq 3$
Vector-Like Quarks (VLQs) of mass $m_{Q}$: $T$ vector quarks transforming as
$({\bf 3}, {\bf 1}, 2/3)$ and $B$ vector quarks transforming as $({\bf 3}, {\bf
1}, -1/3)$. Requiring stability of the finite-temperature effective potential,
and assuming $m_{t}$ equals its mean value, we find that the upper bounds on
$m_{Q}$ for $T$ quarks are 5.8 TeV (for $n_{Q} = 2$) and 55 TeV (for $n_{Q} =
3$). The corresponding absolute stability upper bounds are 4.4 TeV and 29 TeV.
Small upper bounds are obtained for $B$ quarks. For renormalisation in the
Einstein frame (Prescription I) the predictions are almost indistinguishable
from the classical values: $n_s = 0.966$ and $r = 3.3 \times 10^{-3}$.
Renormalisation in the Jordan frame (Prescription II) predicts larger values of
$n_{s}$ and $r$, with $n_{s}$ generally in the range 0.980 to 0.990 and $r$ of
the order of 0.01. The predicted range of $n_{s}$ is consistent with the CMB
range obtained in Hubble tension solutions which modify the sound horizon at
decoupling, whilst the predicted values of $r$ will be easily observable by
forthcoming CMB experiments. The observational upper bound on $r$ generally
imposes a stronger constraint on $m_{Q}$, with the $T$ quark upper bound equal
to 2.4 TeV for $n_{Q} = 2$ and 13 TeV for $n_{Q} = 3$. We conclude that
VLQ-stabilised Higgs Inflation with Prescription II renormalisation favours
1-10 TeV vector-like quarks that will be accessible to future colliders, and
predicts a tensor-to-scalar ratio that will be observable in forthcoming CMB
experiments and values of $n_{s}$ that favour an early-time solution to the
Hubble tension.
